I have 245 series in front, and i'm extremely satisfied. I wanted to get rid of my 305 on rear, but didnt want to change my Oz wheels for wider (and rarer/more expensive).

So i took a chance and ordered the relatively inexpensive Continental Extreme in 325-25-20 size even though it should've worked on 11.5''+ width wheel only. So i now have a similar tires set-up as the GT2RS, but on 8.5/11'' width wheels. And it doesnt look weird at all, in fact it's pretty much the same look as the GT2RS except i have 20's on rear wheels.

Just installed it, but so far the traction is excellent and no issues when cornering hard. Will post picture later.

 

Wanted to do the same thing as you did- how has it worked out these miles/ months later ???
Thanks
mark