3"s is reasonable. I'll have 4-5" easily once the pads are in the seat. I plan to wear a light helmet at all times anyway.
Jury is still out on the seats for me. Suspension seats are nice for puttin' around but when it's time to get serious and you are pulling your belts down tight, how much give are your seats gonna have anyway. That and as the seats gives and your belts loosen, what problem does that create. This is one aspect of suspension seats that I never liked. I always felt like I was having to tighten my belts and then when you go to get in next time they are too tight to fasten. There is also a HUGE difference in ride quality, and therefore comfort, between air shocks and properly set up coilovers.