Sounds like we may have crossed paths.
i was in escondido/san marcos,, back then,,(with a short stint up in Sac)
and most always on Honda's at that time..
then moved to the midwest,in 84ish ,but to this day still visit socal often..
If looking for straight line stabilty i would go with the 06 thru 08 KX500AF (as far as Service models) as they were built on the 450 chassis..
(or build your own on a 450 chassis )
The Service 2009 model is on the 250F chassis and is very stable,,
but if straight line was a concern, i would go with the 450..
and yes they are rock stable in my opinion!!
i'm sure Dusty Rabbit would dig the 500AF's ,
as he still is a fan of the old KX500's, and i' msure still has a few of them around in fact..