Heres my view and perhaps Chris can yay or nah it...
If your car is running 13's at 110mph or less, than your car is quick because its getting out off the line very well. If your pulling 13's at 125mph, your car is running SLOW because of traction issues. I.E. FWD turbo cars.
I dont see a problem with a 13.0 car not wearing a helmet as long as its not breaking 110mph. But if your trapping 110 or better, your car has a lot left in it if your only pulling 13's, and you need to wear some sort of protective gear.
Ill enforce anything that Chris asks me to, and well tech pretty thuroughly, but somtimes a judgment call needs to be made for safty, and if i have to make the call, id say the trap limit is 110mph, after that, your wearing a helmet. this only pertains to the cars running 13.0 or slower, making those trap speeds.