Ours came with the Michelin runflats, and we wore them out in just under 30,000 miles. Since my wife is the primary driver, we decided runflats were the way to go for replacement. My only real complaints on the Michelins were the road noise toward the end of their life (quite loud) and the low mileage life.
If I were the primary driver, I'd have opted for the Conti DWS tires. But I'm also willing to mess with a flat tire.
So for us the runflat debate is more about safety than maximum performance. And frankly, it is a 5,000lb SAV, so it isn't really performance oriented to begin with (regardless of what BMW marketing says.....) For real performance, I jump on my Ducati....
2010 E70 X5 35d
Alpine White on Black with Dark Bamboo trim
ZAP | ZCW | ZPP | ZPS | ZRC | ZTP | 322 | 328 | 330 | 386 | 4AZ | 4UB | 655 | 6FL | 6NF
2008 Ducati 1098S Red naturally....