Don't really care about the original reasoning for larger wheels. 20s are much more visually appealing than 18s for an SUV (not just BMWs). You go higher in trim for many models and they usually offer an inch or two larger wheels despite the performance hit. Hell this is even true for minivans. Nearly 7 years later I still look back at my car after I park it - love the look. Tell me that doesn't count for anything.

Nobody's talking about 22s here. How common are they? Not very.

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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