I had my TT350 flat out on the road, and other dirt bikes too ... I've ridden bikes that others have gotten off after having mad tank-slappers and done the same things on the same road with no problems ... so dunno

Just remember that fork braces were used on mountain bikes to stop the forks flexing outwards from each other, under hard braking ... you get a little bit of front/rear control too but really, geometry is the big problem ...