huper optic is nice but not really necessary in NY - different story if you were in Arizona where the sun really beats down on the interior - it would really keep the heat out. I don't have the rear climate package so I just did 35 front and back... I can only guess that it matches the factory tint. It's definitely not 20.

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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