Actually to correct something to go from 1/16 to 0 you are NOT going to see a HUGE difference. Save your coupon. You gotta do something more drastic like 1/8" toe out on the rear WHICH IS UNSAFE TO DRIVE FOR DAILY CONDITIONS!

To bias air pressure like I stated you want the front tires to grip more than the rear to get ride of understeer. Remember understeer is the front tires breaking away before the rear tires do. Oversteer is the reverse.

Different tires have different break-away characteristics. Some work better at higher air pressures and some low. For instance drag tires work better with low tires pressures (usually around 15-20psi), but running those pressures when you autocross and you are going to have problems.

I recommend sticking with the pressures you have now, unless you want to kiss a guard rail or spin out with just lifting off your gas. Use the low/high when autocrossing only since it will be in a controlled environment and in safer conditions.

With 40f/45r you are basically making the rear tires break away before the fronts do, but for the typical novice driver (yes this means you) it will break away VERY quickly to the point of almost snap oversteer. When you run 45f/40r the car will still oversteer but in most cases easier to control AND recover from.

By the way to recover from oversteer I hope you know what to do, right? You turn the wheel where you want to go and add more throttle. This will put more weight on the rear tires to keep it planted.