I just picked up some Gaerne SG10's. Yes they are stiff and it might take a couple motos or a day of practice to get used the feel for shifting and braking, but I'll take protection over comfort and flexibility. It might be vintage, but it's still motocross. When everyone is trying to get the holeshot something is bound to happen. It's not a question of if, but when.
I know a few racers who like wearing "period-correct" gear, but when was the last time you saw someone wearing Hi-Points and a Jofa mouth guard at a National?