Originally Posted by
dddd
In lieu of switching to an 8cm stem, perhaps first try riding off of the saddle with hands in different locations on the bars and lever hoods. This should clarify which direction that you might want to go with stem length, and if the steering "heaves" with hands in all three positions then I would investigate whether the headset is turning with zero resistance about center (holding bike off the ground and nudging the bars slowly with one finger).
You, sir, are discussing a ride/handling theme I've been on about for a few years now. Extremely relevant and naturally not even remotely discussed (except here and there by me, very occasionally). A too-long stem
AND bar reach combination (to say nothing of hood position and length) will make for tiller-like steering the yanks and drops and sweeps in exaggerated fashion due to one's pushing and pulling on the bars when rocking back and forth out of the saddle. I've ridden bikes like that, and it's taxing and very unenjoyable to ride, ultimately stifling the acceleration effort by bringing in muscles from the rest of the body to help and try and control the involuntary writhing around.