Thanks, this is quite helpful. I have no idea about other Sportful bibs, but the Fiandre definitely seemed ok in one size smaller than my Castellis. Of course, the Fiandre winter bibs are made of decently stretchy NoRain fabric, while my Castellis all have the somewhat less stretchy (reinforced) panels around the waist area. And my only experience with other Castelli winter bibs were the Polare and the Meno Wind (both of which were again less stretchy due to the use of Windstopper panels).
I’m just surprised that the size M Sportful Fiandre Pros fit ok (snugness was more the pleasant compressive kind rather than sausage-in-casing feeling) and they didn’t even require much extra effort to put on (I need to be more careful with my size L Castelli Premio bib shorts in fact). And everywhere I’ve looked online people seems to be saying that one needs to go up one size in both Castelli and Sportful.
I’d rather try on the size L Fiandre too, but the local distributor cannot source them for the foreseeable future and the only online options are much more expensive. So I’m just not sure whether it makes sense to wait 1-2 months (and possibly the size L turning out to be too big in any case) or take a chance with the M and hope that the seams and the fabric will not suffer too much from the snug fit 