Drifting

Good point.

After much online research I've decided to go with 35% tint on all the side windows and 50% on the rear.

35% looks nice and definitely tinted, but will attract far less attention (and tickets) from cops for illegal tint, than if I did a 20% tint, and the 35% won't contrast as much with my windshield, which I'm not tinting.

50% on rear window will probably look like 30% given the angle of the window, and still allow me to check my rear for cars on track and cops on highway.