I may qualify as cheapo of the week, but here goes:
If you have an air supply, just let air out of the rear tires until the rims are 1.5" lower. Step back and look at the car. Go down to 2" and look again. Decide which way you like it best. Or take pics and decide between them.
P.S. DON'T try driving on tires before back up to normal psi.