My calculations for backspace using a 10" wheel 285/40/18 led me to 6.7" to keep about 3/4" from the outer well. I guess I'm off by about 0.7" since 6" is working for you and you are almost 2" taller. It's iffy trying to measure with the wheels loose.
One cool thing about the 285/40/18 - these are under $100! (plus 30 for shipping). I won't mind making some smoke :)
http://ssl.delti.com/cgi-bin/rshop....6&ranzahl=4&nichtweiter=1&pk_campaign=froogle
