I just received Bilstein B6 front setup with H&R sport lowering springs. Given that I have rear only air suspension. I have 2 questions :

1. what to supplement the rear setup given 136K on prob Original equipment. What do most owners with B6 setup have in the rear?

2. I currently have 19" wheel staggered setup. What would be the pro's to go with 20" wheel setup from a performance base?

Thanks

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2004 BMW X5 >4.4i Retrofit 4.8 Rear Bumper, Extended Flares, 4.8 exhaust ,Bull guard, Blacknight gauge cluster.
2009 BMW X5 >35D -Stage 2 DUDMD tune, full delete ATM catted DP, Midpipes, EGRracepipe, swirlflaps.
Sutphin TCU v3.0 Tune *Upgrade ATM FMIC
2005 Audi A4 B6 GIAC Stage 5
*to be installed