20's IMO look the best for an e60. As long as you get the right setup your ride quality should not suffer. Also the roads down the South Bay are pretty good which help.
2009 AW 535i
-Sport, Premium Package, and Comfort Access
-20" Forgestar F14 Black Gloss, Cobb PTF E30 map, KW V2 CO's, Remus Sport Exhaust, BMS DCI, RPI Scoop, Full Front 3M PPF, 35% tint all-around, Orion V4's, Bruce v6.1L cables, LED interior lights, WeissLicht License Plate LED, Trinity Smoked LED side markers, Bimmian Smoked Reflectors, OEM black gloss grills, and Invisibulb turn bulbs.