Originally Posted by AGS
+1. I'm running the 255/40/19 square set-up with Bridgestone Blizzacks (precursor to the LM-60s) on my E60 M5 with great results.
I'd prefer to go with 19s for a winter set up as well, but apparently no aftermarket vendors will guarantee fitment with a 19-inch wheel. That leaves you with the stock 19s from BMW as your only choice. For the money, you could go BBS or HRE, but then you're on your own if if they don't fit.