Lest anyone doubt that PST defenders believe that Jesus suffered spiritual separation from his Father, read these quotes:
Charles Hodge (Systematic Theology, Vol. 2, Part 3, Ch 6, Sec 3): The penalty of the divine law is said to be eternal death. Therefore if Christ suffered the penalty of the law He must have suffered death eternal; or, as others say, He must have endured the same kind of sufferings as those who are cast off from God and die eternally are called upon to suffer.
Loraine Boettner (The Reformed Faith, Ch. 3): We should remember that Christ's suffering in His human nature, as He hung on the cross those six hours, was not primarily physical, but mental and spiritual. When He cried out, "My God, my God, why hast thou forsaken me," He was literally suffering the pangs of hell. For that is essentially what hell is, separation from God, separation from everything that is good and desirable. Such suffering is beyond our comprehension. But since He suffered as a divine-human person, His suffering was a just equivalent for all that His people would have suffered in an eternity in hell.
John MacArthur (The Murder of Jesus, pp. 219-21): To [Jesus] was imputed the guilt of their sins, and He was suffering the punishment for those sins on their behalf. And the very essence of that punishment was the outpouring of God's wrath against sinners. In some mysterious way during those awful hours on the cross, the Father poured out the full measure of His wrath against sin, and the recipient of that wrath was God's own beloved Son. In this lies the true meaning of the cross.
...Christ died in our place and in our stead - and He received the very same outpouring of divine wrath in all its fury that we deserved for our sin. It was a punishment so severe that a mortal could spend all eternity in the torments of hell, and still he would not have begun to exhaust the divine wrath that was heaped on Christ at the cross. This was the true measure of Christ's sufferings on the cross. The physical pains of crucifixion - dreadful as they were - were nothing compared to the wrath of the Father against Him. The anticipation of this was what had caused Him to sweat blood in the garden. This is why He looked ahead to the cross with such horror. We cannot begin to fathom all that was involved in paying the price of our sin. It's sufficient to understand that all our worst fears about the horrors of hell - and more - were realized by Him as He received the due penalty of others' wrongdoing. And in that awful, sacred hour, it was as if the Father abandoned Him. Though there was surely no interruption in the Father's love for Him as a Son, God nonetheless turned away from Him and forsook Him as our substitute.
John Calvin (Institutes of the Christian Religion, Book 2, Ch.16, Sec. 10): Nothing had been done if Christ had only endured corporeal death. In order to interpose between us and God's anger, and satisfy his righteous judgment, it was necessary that he should feel the weight of divine vengeance. Whence also it was necessary that he should engage, as it were, at close quarters with the powers of hell and the horrors of eternal death. ... ... Hence there is nothing strange in its being said that he descended to hell, seeing he endured the death which is inflicted on the wicked by an angry God. It is frivolous and ridiculous to object that in this way the order is perverted, it being absurd that an event which preceded burial should be placed after it. But after explaining what Christ endured in the sight of man, the Creed appropriately adds the invisible and incomprehensible judgment which he endured before God, to teach us that not only was the body of Christ given up as the price of redemption, but that there was a greater and more excellent price—that he bore in his soul the tortures of condemned and ruined man.
Martin Luther (Select Works of Martin Luther, trans. Henry Cole, , vol. 4, p. 365):
We do not by all these observations say that Christ did not suffer in a different way from us, and that he was not tortured and dismayed in soul differently from us, or different from what the damned feel in their dread of, and a fleeing from, God. For Christ even in his own eyes was like unto one forsaken, cursed, a sinner, a blasphemer, and one damned, though, without sin. Because it was not a matter of play, or jest, or hypocrisy, when he said: “Thou hast forsaken me:” for then he felt himself really forsaken in all things even as a sinner is forsaken after he has sinned.
Martin Luther ("A Sermon on Preparing to Die," in Martin Luther's Basic Theological Writings, ed. Timothy F. Lull, p. 422): So then, gaze at the heavenly picture of Christ, who descended into hell for your sake and was forsaken by God as one eternally damned when he spoke the words on the cross, “Eli, Eli, lama sabachthani!” - “My God, my God, why hast thou forsaken me?” In that picture your hell is defeated and your uncertain election is made sure.
Wayne Grudem (“Bible Doctrine.” Page 253-254): The physical pain of the crucifixion and the [psychological] pain of taking on himself the absolute evil of our sins were aggravated by the fact that Jesus faced this pain alone. … Yet more difficult than these three previous aspects of Jesus' pain was the pain of bearing the wrath of God upon himself. As Jesus bore the guilt of our sins alone, God the Father, the mighty Creator, the Lord of the universe, poured out on Jesus the fury of his wrath: Jesus became the object of the intense hatred of sin and vengeance against sin that God had patiently stored up since the beginning of the world.
R.C. Sproul (Together for the Gospel. April 17, 2008. Louisville, KY. Session V - "The Curse Motif of the Atonement," Minute 55:01): What prevents us from seeing God is our heart. Our impurity. But Jesus had no impurity. And Thomas said He was pure in heart. So obviously He had some, some experience of the beauty of the Father. Until that moment that my sin was placed upon Him. And the one who was pure was pure no more. And God cursed Him. It was if there was a cry from Heaven – excuse my language but I can be no more accurate than to say – it was as if Jesus heard the words 'God damn you', because that's what it meant to be cursed, to be damned, to be under the anathema of the Father. As I said I don't understand that, but I know that it's true.
John Piper (Resolved Conference 2008. Session 8 – "The Echo and Insufficiency of Hell," Min 40:00): Hell is all about echoing faintly the glory of Calvary. That's the meaning of hell in this room right now. To help you feel in some emotional measure the magnificence of what Christ did for you when he bore not only your eternal suffering, but millions of people's eternal suffering when His Father put our curse on Him. What a Saviour is echoed in the flames of hell. So that's what I mean when I say hell is an echo of the glory of God, and an echo of the Savior's sufferings, and therefore an echo of the infinite love of God for our souls.
C.J. Mahaney (Resolved Conference 2008. Session 11 - "The Cry From the Cross," Min. 46:35): This moment in Mark chapter 15 [i.e. “My God, my God”], it is this moment, it is what takes place in this moment that delivers us from hell. This agony, this scream, is what delivers all those who turn from their sin and trust in the Savior from hell. On the cross, Jesus experienced hell for us. He experienced hell for us, bearing God's wrath and eternal punishment. And because He did, Heaven awaits all those who turn from their sin and trust in Him. He screamed the 'scream of the damned' [i.e., “forsaken me”] for us. Listen, this scream should be our scream. … This scream should be my eternal scream. He takes upon Himself my sin, the wrath I deserved for and against my sin, He screams the 'scream of the damned' for me.
I am indebted to Nick at Nick's Catholic Blog for assembling these quotes. They are found in a debate that he had with a Reformed Christian over the PST of the atonement (you can read the entire debate here).