There is always a trade-off between higher performance and reliability. Turbo has more moving parts to break, and creates reliability's worst enemy - lots and lots of heat.

Also, this is a new engine to BMW, as compared with the 4.8 which has been used several years in the 6 & 7 series.

I just ordered my X5 4.8i and would do it again, even if the TT was an option, since this is my daily driver. If it was my weekend toy, my choice would be TT.

__________________
Carpe Diem