The 20" rims on the 4.8i are staggered in size so those won't fit the rears unless you buy new rims back there too. Here's what will fit...

http://www.tirerack.com/tires/Select...=Sport+Package

BTW, don't see the wheels you're referring to at all.

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'08 X5 3.0si - Alpine White / Saddle Brown interior
Specs: Sport Pkg, Premium Pkg, Tech Pkg, Comfort Access, Aero Kit, Style 433 staggered 20s on Conti DWS
Mods: Carbon 35 tint, LED angel eyes, GP Thunder 7500k fogs, H&R 20mm/25mm spacers, clear reflectors, gunsmoke-tinted taillights
Coded: Digital speedo, windows/sunroof/tailgate close via keyfob

X5 pics at Flickr