Well I don't know if any of you saw the thread I put about Tanabe needing BMW's for their R&D, but anyways, two of my friends brought their cars in for the R&D session! I of course came with them. The springs are quite nice! There's no more wheel gap, and the cars look much more aggressive.
I ended up driving my friend's 328i back because she had work. I must say the ride was very comfortable and smooth, going over imperfections in the road didn't cause any problems, and the car didn't bounce around everywhere. When taking the turns the car was planted quite well, but since she had run flats the tires didn't grip for beans. I can't compare the stock suspension with these prototype springs though because I've never driven her 328 before it was on springs.
My friend with the 335 says that the car rides much better with these prototype springs than the H&R Springs but I don't know. Haven't driven the 335 so I can't really give you guys any insight.
Here's a link for the 328i:
Link for the 335i:
Just thought I'd share this with you guys. Enjoy!