The way I figure it, that's 1.5% difference in overall pedal travel top to bottom (2.5mm * 2), assuming the distance is measured from the center of the crank arm to the center of the pedal hole. It also would work out to about 1/10th of an inch difference in crank arm length. I have a bike with 175s and another with 172.5, I can't tell the difference... and I certainly wouldn't spend the $$ to replace a perfectly good set of cranks. If I was building something new or replacing a set of damaged cranks, I'd buy the appropriate size, of course.