Not to rain on anyone's parade but when I went up tire size (to 20") on my E60 with a good light, forged wheel (RAC Monolite) there was a definite decrease in ride quality or comfort due to lower profile tires. There was too and increase in performance and handling ( ligher and lower rotational mass).
Have read here no impact on ride quality an decreased performance. My experience was the opposite and wanted to share. Went with lowering springs on the F10 and prefer that for me.
F10 30 Jahre M5/F80 30 Jahre M3
F82 M4 GTS
E36 M3 with S54 Swap/F22 M235 Dinan Stage 4
X15 X5 3.5i/03 Cooper S (Maxi Tuned +50bhp)
60 Impala (43k orig mi)