I'd think that my seatpost would be shorter, if anything, on a larger frame. Don't have a pic handy but eyeballing it looks like there's ~3 inches from the seatpost clamp to the thingy on the seat tube that adjusts the saddle angle (sorry, brain's kind of off), which come to think of it is shorter than what many people run it here.

OP, i think the 53 is worth waiting for, if you fear crampedness. Out of curiosity what were you looking at, exactly?