At 6'4", the 2" kit was the only option for me. You lose the fore/aft adjustment, which isn't a problem as long as nobody else drives your car. My wife is 5'2", so this kit ruled out her being able to drive the car, which kinda stinks because while the high hoodline intimidated her a bit, she enjoyed driving the car.
The 2" kit made my car so much more enjoyable for me to drive it's like a different car. My knee doesn't hit the headlight bezel (as much), and my horizontal sight line is now well below the top of the windshield. I even removed my sun visor to gain the extra 3/4" it cost me.
If you just want a little more head-room, but are ok otherwise, stick to the 1" kit. If you're really cramped (which at 6'0", you're probably not), the 2" is the way to go.