The 4.8 accelerates from stop noticeably (and much) better but everything else is not really a big difference when you're talking in this "handling" context. Body roll isn't different in a 3.0 or 4.8 unless you're hauling ass around a corner just when a light turns green.

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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