Allow me to buck the conventional wisdom.

IMLTHO, unless you are physically at the extremes of the bell curve, 5mm of crank length is going to make very, very little difference. Haggling over 172.5mm vs. 175mm is incredibly silly -- that's less than 1/10 of an inch out at the end of your leg. The angle difference at knee or hip is immeasurably small. Plus, you can easily turn your 175mm into a 170mm or a 180mm by cleat placement alone (or by buying one pedal over another). And that's without talking about the intricacies of saddle and seat post placement or whether you are seated forward or back on the saddle.

I think we (the middle 90% in leg length) tend to take crank length FAR too seriously. There are several other measurements that have a much greater influence on fit.