OK, so I wanted to update this thread with what's been going on for those that might want to have this combo in the future. First, the numbers.
Front: 17x8.25 +25 XXR 527 with 215/40 = 40.8
Rear: 17x8.25 +25 XXR 527 with 235/40 = 44.1
Rear: 17x9.75 +25 XXR 527 with 235/40 = 45.4
Rear: 17x9.75 +25 XXR 527 with 255/40 = 47.4
Front 16x7 Cup 240R with 195/50 R888 = 34
Rear 17x8 Cup 240R with 235/40 R888 = 41
The Advan AD08R runs wide for sure, this is a 255/40 on the XXR 9.75" wheel.
Fitted to the car with a .75" drop and -1.5° they poke a bit, but with some fiddling they could certainly work.
But seeing how little they stretched, I figured I'd try my 235 on the 9.75" wheel, just to see what it looked like. I was wanting something more stretched like the front anyway, not a crazy stretch, but more than the rear had, and this is the result.
Looks more stretched in pix than in real life, and is a TINY bit more stretched than the front 215/40 on the 8.25" wheel. With a little bit more camber, and a bit more drop when my suspension comes in, this combo will be an easy fit with almost no work at all.
This is a little photochop I did showing the difference between the 8.25" wheel and 235 on the left vs the 9.75" wheel and same 235 on the right. Again, in pix it appears more stretched than it is, in real life it looks quite nice.
My final thoughts are that there is no way I could go back to the 8.25" wheel in the back, the 9.75" looks MUCH better, and has a much nicer concave to it, especially compared to the front. With regards to the tire, the 235 is absolutely fine (and before you call foul, remember that the Singer Porsche that you drool over every day has MORE stretch than this combo has), but the 245/40 might just be the perfect tire.
We will see