172.5 is worth a try since the guy who fit you recommended it (if he hadn't, then I would say not to switch). 5mm is the minimum needed to see a noticeable difference imo.
Years ago, I dropped from 175 (6'0/33" inseam) down to 170 when I first got my (very agressive) bike fit and it allowed me to immediately run much better off the bike with less fatigued hips and calves. Since then, I changed all my bikes to 170 and have recently found I don't like it. I'm actually making more power on 175's on my road bike and the 172.5 that came with my gravel bike seems to be fine as well. But now, when I'm not in aero on my tri bike I find I don't like the shorter cranks (but since I always race in aero, they will stay).
You just have to find that right size that works for you and for the position you want.
-Bryan Journey Travel Blog
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