I don't think a race between that 550 and the GXP would ever be in the bimer's "favor". For one, they weigh about 400 lbs more than the GXP, they have slightly less HP and slightly more torque, but 1/4 mile times seems to be in the 13.0-13.2 range trapping 107-109. 0-60 is 4.8 for the auto (8 speed helps alot) and 5.1 in the manual. If anything it'd be a close race w/ the edge to the GXP.
You got headers, a tune, and a damn cam and like I mentioned, weigh 400 (probably more like 450 cuz I bet she had the auto) lbs less- i don't care WHAT the elevation is, that's a recipe for disaster every day of the week and twice on Sundays for that 550.
Now the new M5? Fughgetaboutit!!!
'08 GT sport/premium, tints 20/35, 18" TSW nogaros w/ bridgestone blizzak winter, 19" sport oem w/ hankook evo summer, Philips crystalvision bulbs, debadged, Vararam OTR, JBA 1-3/4" LT's, ported TB, MF axlebacks, MF X-pipe, DBA-powerslot brakes, russel SS lines, hawk ceramic pads, GXP shocks/struts, lovells poly strut mounts, Slowhawk Tuned 344/356
Gone -'04 GTO A4 2.5" custom exhaust, sweet thunder muffs, H pipe, Z06 heads, Baer brake it, 20% tints, torrid red, AEM brute force intake, tuned