dakrat,
you will generally want to run your rear wheels about 2.5mm bigger than your fronts. as this gap closes (rears usually wear faster than fronts) you will find the carr will get more twitchy and difficult to drive - more steering. If the stagger between the front and rear tires is bigger then you will push a little more. recently I have been running purple front and white rear which pushes a little. I let the stagger reduce a little to assist my handling.
Chris.