Ideally, you don't want to run your car down to 3.0 mm. You wan't to have a decent amount of ride height of say 4~5 mm front and rear. Too low will cause the chassis to scrub the carpet and cause the car to handle poorly. I run my F1 rubber height at 4.5 mm front and 5 mm rear.
A higher ride height will allow the car roll more and give more weight transfer to the tires.
Skim over various F1 setups on Petit RC and you'll see most, if not all guys are running 4 or 5 mm ride height.