fwiw, recently i have tested a m3 and my 335 back to back at the same corner a few times
both cars have the same tires (bridgestone re71rs, 18 inch wheels, 255/265 on 335, 245/275 on m3)
similar mods
(m3 has stock front control arms, full set hardrace rear control arms, nitron r3 suspension)
(335 has turner monoball m3 front control arms, full set hardrace rear control arms, turner solid alu rear subframe bushings, mfactory lsd, stock sways, ast 5200 suspension, rear poly top mounts, solid bottom mount)
difference... alignment and spring rates, the m3 is a 8/10k spring setup, running stock front camber/toe, i think -2 or 2.ish camber in the rear, i am running 9k/14k spring setup, -3 front camber and -2.6 rear camber
with dsc off
m3 will understeer at the limit (as expected), front and rear feels planted and communicative the whole time, however, i could not put the power and have the rear step out and have to lift until the car stops understeering
my 335 is setup to oversteer at the limit, front feels pretty similar but the rear..theres room to improve on compared to a m3
with that being said, i have the rear m3 braces sitting at home, i am just waiting for the ultraracing center brace to come so i can get it installed
i also got the hardware sitting at home to make and install the the front subframe braces like the one in the first post
dont hold your breath for an update though, i will eventually get around installing it... but ive been lazy and playing with other stuff