For coilover spacing.... I've got 16x8 +30 wheels with coilovers. The wheel sits about 5mm away from the spring, but the sidewall of the 225/50/16 sits about 1mm away. The tolerance is so close that loosening the strut bolts and rocking the spindle out or in is the difference betwen rubbing or not.

On the other side of the wheel, the shoulder of the 225 was barely rubbing the tabs on the fenders that hold the plastic liner on. Looking straight down over the unmodified fender, you see about 3-4mm or tire. This is with camber set at 0* on the camber plate (prob 1.5* of actual camber). If you ran a 225 on that x9 +35 wheel, the shoulder would actually be 5mm farther in the fender, with the added stretch bringing the inner sidewall 7mm farther out from the fender.

So yeah, x9 +20 would be about right on a 20mm fender with a 225-235, and you could run normal camber.