When I bought my 11 M Sport (with oem M 19s) it came with 255/50/19 Bridgestone Duelers all around. It was a CPO vehicle and the tires don't appear at all stretched on the rear, so I think running 255s (at least this particular tire) all around should be fine.
With that said, I am looking to switch to a dedicated summer/winter set just due to the fact that I would prefer a wider, staggered setup.
Current: X5 50i // Space Gray // M Sport
Past: E90 M3 // Jerez Black // 6MT