I think you would have a tough time fitting anything wider than a 7.5 inch rim.
You might squeeze an 8 inch with a 225 at the very most, but I doubt it. I would stick with a 7.5 and a 215 or 225 at the very most, and even then you may need a slight fender roll.

 

Going to anything with a 225 is going to require a fender roll, even on a 7.5 inch rim; have you done any suspension work?
An 8.5 is going to be way too wide, and you won't be able to put a tire wide enough to necessitate that wide of a rim.....

 

My BE is rolling on 17x8 +50 w/ 225/45/17. No issues at all and the car is slammed on CUSCO's.

 

BE's have WAY more room than BD or BG's. I have 235's under my BH.

 

No way, unfortunately. Any hub adapter that would allow the larger bolt circle would add so much offset that you'd rub even if you were running 185/30/18's.

They'd seriously stock out at least an inch from the body. I know it sounds like a killer deal, but you should pass, unless you want to buy them then sell them to a 05 STi owner

 

Yup, STi 070's were a stretch, literally; my rear fenders are flared more than a half-inch for clearance.

 

Ya, BE's do have alot more fender space. 225's fit under there like nothing. The 98 would be more like the GC Imprezas in that it will have some limited space issues in the fender well.