My friend said the same thing he wanted to mod his but not much is availible he wants a smaller pulley and a tune, then a a modual to lower his rig. He said everything is super expensive (worse than ///M tax) because you are limited for options so they can charge what ever they want. He did get a decent set of wheels but aside from that its pretty limited. As for the performance stock we have a buddy with a 50i and they were pretty close in the two races they did the 50i still edged the RR out but just by a bit. I am a mod addict even the lack of options for the BMW frustraights me so the RR would be maddening although a nice set of wheels sets you apart from the crowd RR seem to be either stock or a "rappers delight" with huge chrome wheels and a strut package on them.

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X5M Eisenmann exhaust, de-Catted down pipes, 22" HRE wheels, ECUProgram stage II (700hp) tune
X5 35d Tuned and Lowered