I had a Guy come out and install 16x8' bulbs in my 24'x36' shop...it looks like an operating room in there now...
I don't think you can ever have too much light. I painted my old garage walls white about 5 yrs ago and have 3 twin 4ft. floresent fixtures. Made a great improvement over what I had; I cud'nt believe how much difference at night w/ the light reflecting from painted walls. Was big improvement even w/o the flo. fixtures. Although I don't work on the car now unless it's dry sunny day, painting the walls made improvement for lot's of other uses or things I do in the garage.