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.