I have staggered tires. 225/45 & 245/40. I am going to go 245 all around here in a few miles. (the fronts are almost done)
I had staggered rims & tires on my S2000 also. The S2000 came staggered, unlike the FR-S.
Here are some of my thoughts...
I would either go 225/40 all around on the 8.5's or 245/35 all around. 235/40 is taller, and a rare size. (OK semi-rare)
Staggered wheels and tires look awesome! I like wider tires on the back. If this is the look you are going for, Do It!
I don't think a stock FR-S (200hp) is going to benefit from being staggered or 265 width tires. (you said no AutoX or anything like that)
A staggered setup is going to lower your mpg and acceleration. The rear wheels and tires are going to be heavier. I have listed a few sizes below of Michelin Pilot Super Sports. As you can see the 265 is 3lbs heavier, the 9.5 is also X-amount lbs heavier. So the rear is, lets say 5lbs heavier, you will notice this compared to a lighter weight wheel and tire combo.
GOOD LUCK!
MPSS tire weights: (per tirerack)
225/40/18 = 22lbs
235/40/18 = 23lbs.
245/35/18 = 23lbs.
265/35/18 = 26lbs.
This tire calculator really helps get the same size (or close enough) outside diameter tires for a staggered set up. Or for plus sizing.
http://www.discounttire.com/dtcs/infoTireMath.dos
tire weight Linky:
http://www.tirerack.com/tires/tires....omCompare1=yes