275/40/18? you sure you didn't want to do 35 profile? 40 profile on a 275/18 is quiet tall!
best setup for my S14 so far is what I have now.
18x9.5+15 255/35/18
18x10+38 265/35/18
such grip, so push, much fast cornering
and I would suggest you do 255/35/18's in front as well, about same amount of tire patch as 245's, except it fits better so you don't have to have so much camber/rubbing issues.
http://www.rimtuck.com/search/thumbn...allf=35&sort=1
check out some pictures of cars with said tire sizes on the link above. useful tool.