We run SLR's in the 12's with the red car on a 29.5x10.5 tire(not W)with no issues running 7's. Dont get caught up in "ideal" numbers every combo is different. Might have to work on the car a bit to make it work but if you have an ET goal you are gonna have to work to get there anyway.

I also run 8's with a 3600lb 64 Plymouth NA and my SLR is 10.4 and still on the 29.5x10.5 tire. Its not rocket sceince.