Were both talking about whether that particular bike model and size was to big for you or might one of them just be talking about that size in general and not considering the geometry of the specific bike?
If you like being stretched out you might like the M54 size.
Also, bike fitters don't always fit you for the utmost in comfort. Some go more for putting you in a position to maximize your power for the distance and effort you put in to your rides.
There isn't one bike size that is correct for every person with your body dimensions. Usually you can fit a range of sizes pretty well, IMO. So until your fitter knows your personal desires for a bike, I don't find it odd for two different fitters to have different opinions just like we do. I've fit well on bikes from a 64 cm to a 56 cm. So I'd never say one size was the only size for you.
Were the biomechanist trained in bike fit? Not every biomechanist is a bike fitter from the brief introduction of the term I just read after googling the term.
Last edited by Iride01; 01-01-23 at 01:43 PM.