Another data point, my current bike (L Cannondale Scalpel SE) has a reach of 442mm, I've got a 60mm stem with the bars rolled forward to give me more length, but combined with the relatively slack seat tube angle even with the seat all the way forward on the rails you have to (literally) lie over the bars to keep the front wheel down on steep climbs. Guess why I think I should have picked the XL, although tbf it's only got 8mm more reach.
My new bike is 60mm longer on the top tube, but the stem is 32mm.
On my 56cm road bikes I'll run a 120 or 130mm stem.
Another data point, my current bike (L Cannondale Scalpel SE) has a reach of 442mm, I've got a 60mm stem with the bars rolled forward to give me more length, but combined with the relatively slack seat tube angle even with the seat all the way forward on the rails you have to (literally) lie over the bars to keep the front wheel down on steep climbs. Guess why I think I should have picked the XL, although tbf it's only got 8mm more reach.
My new bike is 60mm longer on the top tube, but the stem is 32mm.
On my 56cm road bikes I'll run a 120 or 130mm stem.