We decided to find out, though our bikes are now dirt trackers. The boy needed to practice starts with lights, just like the pros use at the dirt track and for $15 bucks we made a dozen or so runs each at Thompson Raceway last night.
2006 YZ250f - 13.97 @ 89mph
2004 YZ450F - 13.24 @ 96mph (ran out of gearing though, bouncing of the limiter)
And just for completeness
1974 RD60A - 24.29 @ 53.8 mph
2006 YZ250f - 13.97 @ 89mph
2004 YZ450F - 13.24 @ 96mph (ran out of gearing though, bouncing of the limiter)
And just for completeness
1974 RD60A - 24.29 @ 53.8 mph