Samwow, how the F do you go through a set of rears in 4-5 months?? I put mine on in Spring of 2010, rode all summer on them, then put them on again this year and there is still plenty of tread left on all 4 tires. None are wearing unevenly. I am on stock ZHP's 8x18 in front, 8.5 x 18 in back. I can tell you this though: when I had the SSR GT3 reps, they were 8.5x18 front and 9.5x18 rear, and had the exact same issue as you, rear inside corner was rubbed almost bare, while there was plenty of tread left on the outer edge. Same tire sizes as on the ZHPs. IMO, putting 255/35's on a 9.5 inch wide wheel will indeed stretch the tires and rub the inner edge ridiculously. I have pics I took of all 4 tires while I was dealing with my UUC TSE3 leak (story for another day). Rears are good all around, as are fronts, and no uneven wear. And I did the alignment in my driveway by adjusting the tie rods and driving around the block like 500 times!!!!
MightY, I am a 100% believer that unless you're near some REALLY steep roads, putting winter tires on your bimmer is a waste of money. Use All seasons, they grip fine, don't get all crazy, and they last twice or three times as long as winters!