[Tilt]

If X > 10% of min or my opponents stack, its always, always, always AI or fold. I use the Eastbay formula, and I have to tell you, it works really well.

If its less, then it becomes opponent and hand dependent. I don't think you could construct a simple rule.

Will your opponent let you see flops in unraised pots?
Is your opponent very good at HU aggressive play?
Can you get him to fold easily on the flop or turn with any two?
Is your starting hand one that could be a useful trapping hand against a reliably aggressive opponent?
Is your hand a monster, and your opponent a bit over aggressive, such that a limp/reraise might work?
What range of hands will your opponent call with preflop, against what kind of raise?

All are considerations, there are probably many more...