Trigger, the fact that the frame is 57cm and you're 5' 11" means very little, although some would have you think otherwise.

For comfortable riding I (and all sensible cycling books until the tiny frame business came around) would suggest having between 3 fingers and a fist worth of seatpost showing, this could leave you on a frame somewhere between a 56cm and an 65cm.

For instance, I'm 6', maybe 6'1 on a good day, today's bike store would have me on a 56cm or maybe 58cm frame, because "that's what 6 footers ride today"(apparently). However, I'm most comfortable on a 64cm frame, this seems ridiculous to x bike shop(mostly because frames don't come this big anymore), but it doesn't change the fact that this size of frame is the most comfortable for me.

Comfort comes first, this spouting of rote numbers is irrevelant, although sadly much practiced.