I run real low (single digit) pressures in DEEP snow to get up on top of it, but for a couple of inches on the road I run normal pressures. If you are travelling at any significant rate of speed then you are better off cutting through the snow than being on top of it. Go easy on the throttle too and keep the revs as low as possible without lugging the motor.

Harry Wagner
Harry Situations
4x4Wire's Toyota Section