I'm having a custom frame built. Like pretty much everyone else I've been riding 170 mm cranks, but with my 34 3/4" inseam, I'm considering asking to have the frame optimized for the 190's that the various online formulae agree would be proportionate for me.

My question is this. Given that this is a once in a lifetime sort of investment, should I decide that I'd really rather be on shorter cranks, how much compromise would it be to be riding, say, 170's on a frame designed for the longer ones?

Thanks