You're rubbing at stock height on your 20s? Is it because your wheels are almost flush with the outside of the fenders?..... because they dont tuck?

 

I've got 20's on 35 series all around...NEVER rub...VDC works just fine...stock height. Visually it looks like I can lower at least 1" w/o a problem.

 

with the sizes you said those wheels come in I would go 245/35 up front & 285/30 in the rear if you're going to lower it also go with coilovers you can get the tein basics for a little under $800

if you really want to go with a 35 series in the rear you can go with a 265/35 but personally I would never do this the tire would be really stretched

 

I'm currently running 285/30/20 and 245/35/20 on my coupe. It's stock height and I have no rubbing issues whatsoever. btw...this is on 20x10.5 and 20x9.5 wheels.