The difference between the #2 and #3 pads is exactly 5mm and will be visible by the gap between the tire and fender. If you change the rear spring pads into #2 pads, the gap between tire and fender will be 5mm smaller...
The difference in the thickness of the pads is exactly the difference in height of the car's chassis above the tires.
Personally I like the side view of a car that is lower in the front as in the rear...
with a minor 600+k