To be honest I am amazed that anyone thinks the RFT's offer superior performance to regular tyres, lets not forget that BMW's M/// division to date has always shod there cars with normal tyres even when regular cars in the range have RFT's. Maybe the performace version of the X5/^ will change that.

Of course tyre "performance" has many different characteristics ride, road noise and grip (both wet and dry) being just three of them. The performance of RFT's in the UK when combined with our roads is very poor I certainly noticed a huge improvement in the ride on my old 535d when I changed it to regular tyres and I will do the same with my X5 when the time comes.