I would go with 18" and throw snow tyres on them. And grab aftermarket wheels for summer...

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04 Porsche Cayenne S SW(Retired): 22" HRE 645R, Frozen Rotors, Techart Sport Muffler, Twin Tailpipes, Fabspeed Bypass, Techart Turbo Full BodyKit, Magnum Hood, Headlight & Taillight Covers, Eibach Springs, BMC Airfilters, Tequipment Roof Rails, Roof Strips, V1 Hardwired, Silver Hood Crest, Clear Marker

08 BMW X5 3.0si AW: 22" HRE 996R, GP Thunder 8500K H8 & H11, ACS Full BodyKit, ACS Sport Muffler, Racing Tips, M-Tech Flares, Running Boards, CF Roundels, H&R Springs