Thanks alohasurftoad, johnung, jvac, and oksymoroni for these replies, so much good information you've shared.
I guess I'll need to reevaluate things as I wish there was a nice wider option available for the F34 platform. I was next to a new X5 M50 and that thing had 22" in the rear, 315 cross section tires. They were so wide
I still think 19" is the way to go for the F34 platform, so perhaps square 255 is the way to go (potential for some rubbing), or, if I want that wider look tire in the rear, will have to live with the downsides of a staggered set-up.
Even the M3/M4 I believe doesn't go much wider than 275 or 285 in the rear, so perhaps I need to just keep that in mind.