Adams and Schwartz actual ran the math in their recent
bluff article (Nov., p. 106), and came up with 8.5% as being about the amount you should be willing to call to crack AA/an overpair.
Their article reminded me of
this thread, so here are the percentages of your stack you should be willing to call off to crack AA, depending on your hand (note that this is where AA open shoves every flop, and these are the "win %" for the top
hands that called):
66-99: 8.7%
JJ-KK: 8.6%
TT: 8.5%
22-55: 8.4%
87s, 76s, 65s: 4.1%
T9s: 4%
98s: 3.9%
97s, 86s, 64s: 3.7%
87o, 76o, 65o: 3.4%
J7s, JTo: 3%
Q9o, 43o: 2.7%
K5s, 72s: 2.1%
Aks, A5s: 1.9%
A8s, A7s: 1.6%
AKo, A5o: 1%
A8o, A7o: 0.7%
Conclusion: you really shouldn't try to crack them unless stacks are VERY deep.