I have to agree with your observation on the RFT & performance issue. (I am still not sure there is even one issue) My Protenzas have 21K on them. the fronts are good for at least another 6K, the rears have maybe 1.5 to 2k left tops.
I have seen several references to BMW engineers adressing the issue of handling given the stiffer side walls of the kevlar reinforced RFTs. Seems to me the car is designed specificly to roll on RFTs. Rolling a non RFT may change the handling of the vehicle.
These cars are incredibly complex pieces of engineering. I am not prone to mess with somthing...I would love to test drive a 330/335i ZSP car on NON RFTs to make up my mind for myself
The big down side is we are stuck with only one option of RFTs when you have the ZSP package.