if you go lower then 2.5 you should be shot! at that much, you can not hit any sort of bump or else you are fucked, you cannot turn b/c your tires will hit teh wells, and it looks totally gay! i would say 2 unless it is for show.
2 inches!!!!!!!! thats way too much im telling you if you want to lower your car and still be able to drive it you lower it till the control arms are level with the ground. its a little more than 1 inch. get bigger wheels if you want to kill the fender gap. i would reccomend that you buy a set of springs that lower it a inch or a little more and that you cut 2 inches off your stock springs for when you want to slam it. the stock springs will ride like shit when they are cut...but hey you were talking about lowering it 3 inches...that would leave about 1 inch shock travel. you dont have to listen to me but its not like i dont work on cars for a living.
My car is lowered by 1.6 initial, 1.77 after the springs have settled. Neuspeed Street Pro.
How much lower could you possible go, without burning some RICE? My friend has a civic and he got himself cheap APEX springs.
See below how it looks. 2" drop. He cannot have any people in the back of the car. Also the stupid dealer who sold him the car, told him to just burn off the rubber from the wheel well with his tires and then it should clear. What a loser...