I'll also add that against someone who has a range of AK/QQ+ or similar, I might go as low as 10:1 in implied odds in position (I stress in position).

Say a mega-nit-fish raises big from UTG, and I'm on the BTN with 77, I'll call with 10:1. Also, imagine a player who isn't a nit, but only 3bets AK/QQ+ my BTN raise from the big blind, I'll call with 10:1 or better.

In either scenario, if I don't flop a set, but the board doesn't contain an ace or a king (even better if it's queen high), I can call his continuation bet with my underpair in good conscience knowing that I have 40% equity against his range, and that he'll check his AK on a non ace or king containing turn so that I can float him. If he's not the type to c-bet a missed AK after 3betting (this is rare even for a nit), great because his hand will be face up. If he's the type to double barrel his missed AK after a 3bet, that's fine (not desirable, but still okay) too, because we still have odds.

And if I do flop a set, well gravy. I'm getting his stack nearly 100% of the time.