Largest tire size for 20's?
 

Is it possible to run 285/35/20 in the rear and 245/40/20 in front?

I don't have a sport suspension...

I'm pretty sure no.

no 245/35/20 barely fits... it was rubbing mine with h&r sport so i had to roll fenders...

and biggest for rear is 275/30/20

no.

I don't have sport and I have 245/35/20 and 285/30/20. I have not experienced any rubbing from the rear, just the front if I break the wheel all the way when turning.

I am way lower on coilovers, and my tires are:
F - 245/35/20
R - 285/30/20

Rear fenders are rolled, no tire rub at all really.

The right tire size for a E60 is front 245/30 and rear 275 or 285/25 20".

correct, these are the recommended tire sizes according to rolling diameter. we, and some others, suggest to run with sidewalls 35 and 30 though to have thicker sidewalls for more rim protection. these sidewall sizes are what is usually put on 19" diameter wheels for the e60. if rubbing were to occur, rolling/shaving the fenders should solve that problem.

I can confirm, I also don't have sport and I'm running 20" Staggered Wheels 285/25r20, 20x10 Rear, 245/30/r20 20x8.5 Front. I've had these wheels for more than a month now and have never felt any rubbing whatsoever.

275/30/20 rear
245/30/20 front
sport suspension

no rubs and on the borderline of being too big, perfect fit almost.