By the way guys, it's not 2.5mm. It's 5mm. You adjust the saddle down 2.5mm so you can reach the low crank with the same extension, and the high crank will be 2.5mm up as well. That's 5mm more crunch.

As I understand it, most people are okay within 2.5mm of their preferred length. So, if the op really likes 172.5 the 175 probably won't bother him much. If he finds 172.5 to be a touch on the long side and would prefer 170, then the 175 may just be too much.