I ran those size tires on my E46 M3 after having stock sizes and I was sorely disappointed. All the point and shoot feeling the M3 had was gone with the large size tires. I would discourage it.

I would try to surf the net for (4) 18" M3 rear tires to shod with 255/265 tires and use them just for autox. The fronts will stick out some but won't rub.

Good luck.