I suspect whatever you are feeling is due to geometry and tubing, since you've approximated components. A 1 cm higher BB is a HUGE difference: the difference between the BB height of a road and a track bike. The Peugeot should feel much less stable, straight line, climbing, whatever. But you can probably pedal through any turn, right? Have you ever ridden a pre-war balloon tired cruiser? Super low BB. Guaranteed to drag a pedal when cornering.

Get a protractor and measure the angles. A more detailed description of ride quality would help. e.g. "The Merckx is snappy when I stand out of the saddle on a big hill..."

Cheers