Thanks for the quick responses and the effort. Unfortunately I can't see an improvement in nightly 1f46da0, the steering is still nowhere as responsive as it was in FBA.
Here's a little experiment you can do to see just how sluggish the steering has become. The specific ROM I'm testing is Power Drift (World, Rev A).
Insert a coin and see how many times you can move the course selection cursor with the arrow keys from one side to the other (A to E, then back to A again) before the time runs out.
With FBA I can do this 13 times, with the current nightly it's down to 9 or 8 depending on the speed setting of 0x700 or 0x800 respectively. I see no improvement with other values.
You mentioned that bugs occurred in the game because of the steering; I play this game often and intensively and the only bugs I've seen are:
(A) rarely I'm listed as second place even though I'm clearly ahead of everyone else (and the car behind me finishes after me and gets #1), and
(B) in the Extra Stage with the fighter jet, sometimes the first three AI cars run at full speed and it's impossible to pass them so I finish at #4.
Are these bugs related to steering? To be honest they hardly bother me.