Great thread. I'm genuinely disappointed with the lack of a decent footprint for the M2.
Have you looked at the BFG R1?
It should be available in 285/30/18. I use them on 18X10 wheels all around on my 1M, and on my car the 315/30/18 fits out back on a 10.5" wheel. .
I have found that the shoulder design of the BFG helps allow a lower, wider tire.