I voted 275 / 285. As previously stated, there is no reason to run a square set when you can't rotate them anyway. I'm always for running the beefiest tires you can. If the PSS are less expensive then it's a not-brainer to get them (great tires). You may need some camber to run the 275 in the front. If you have KW coil-overs you will also need a 5mm spacer in the front to clear the helper spring.
'13 M3 - Silverstone II - Sold
'04 M3 - Jet Black - BBS E88, KW Clubsports