Greatest size rotors would be the 294mm as far I can recall correctly. WRX rotors should be of the 289mm variety. Checking the Pink holy book says about the same thing. I suspect that you could conceivably go 330mm, however, then you have issues in that you're really not taking advantage of all the greater space afforded by that size rotor. and not to mention also wheel clearance issues.
I will take pics later on tonight.
Like I said,I really dont want to separate these, as I already have stainless lines.