Personally, if your not using a 100-110mm stem, your on the wrong size bike.
Floor-to-pubic bone measurement, is the best guide.
Standover clearance, is overrated.
People sizing bikes, by the top tube length, It doesn't work. Might wonder why you are going for a new frame 2cm smaller top bar, but can only
think that your current frame is too big (by PBM) and this means the seatbar may be shorter, too?
On a bike with a 73.5-degree head tube, lowering topbar 2cm, brings it brings it forward 0.75cm, also.
Maybe just try your original stem, in your new bike and go from there.
have you measured your Floor-to-pubic bone measurement?
Just some thoughts.
Cheers

Lone Rider- I rode on the long, dark road... before I danced under the lights.