With historical perspective, it would seem that a shuffling in prestige (or at least identifiable academic standards) can occur across time:
SAT Tiers (circa 1960)
Amherst/Williams ~= Columbia, Harvard, Princeton, Yale
Hamilton ~= Brown, Cornell, Dartmouth, Stanford
Bowdoin/Middlebury ~= Duke, UMichigan, Northwestern, UPenn, Tufts, UC-Berkeley
Colgate ~= UColorado