Just had a blast yesterday at the Performance Center CCA autocross in the M3. Mike driving the F80 and I were battling for FTD but I had the tire advantage
. My car has the original Dinan non-adjustable bar (65% stiffer than stock), pins out max camber up front, and I was using 10x18 ARC8s with 275/35 NT-01s. No understeer problems for me! The car was essentially perfect. I was instructing and giving ride alongs, and numerous people couldn't believe how well balanced it is. In fact, I can't fathom driving this thing with the stock front bar as it would be way too loose on the high speed turns there I would imagine (with the square 10"/275 NT01s).
(note: I've never driven it super hard on my street stagger 19" (255/275 PSS) as my F-street setup is 275 Rivals all around on 18s and then I have this square NT01 setup).
I'm guessing your issue is old tires/stagger setup/overdriving the front end? I can't identify with the Miata transition since I've been autocrossing/tracking BMW sedans including my heavy M5, for, well, since forever ago (closing in on 40 years of this stuff pretty soon
).
EDIT: BTW, that chattering from the front PS2s likely means they were overinflated...anything over 38 hot or so is probably too high. Then again, they could be well heat-cycled also...