To 'levirola'. :
I have almost the same tire/wheel combo. My car is on eibachs/Tokico illuminas II with TEMS.
-I run a 275-35/18' in the back on 18x10 rims with 24 ET : Rolled rear fenders with a slight pull. ( 0 camber)
It rubs very little on hard bumps,and a little more when I have 2 more persons + a full gas tank. (gonna install some Tanabe sways soon)
-and 235-40/18' infront on 18x8.5 rims with 25 ET : Stock fenders ,no mods. ( 0 camber)
Fronts aren't rubbing. I could use a bigger tire like 245 or so.
For me the best offset for a 18x10 rim with a tire size 275' for the back without rubbing on stock
fenders will be a +35 ET. For a rolled fender will be a +26 ET ,and for a rolled+slighlty pulled fender a +22 ET and
all that with 0 camber. I use Dunlop SP9000 tires.