hey Quad,
have you heard of this race?
http://www.parisancaster.com/they used to dub this as a mountain race but the focus has changed to more of a cyclocross race.
you get 20% mountain bikes and 80% cyclocross. It's in April and is perfect to launch a season.
it's hell if the weather isn't great, which is almost every year.
I've done the 70k (used to be 60K) two or three times. while it's a great course, it's expensive and you get a crappy Subway sandwich. We still get plenty of people from our club doing it.
you get plenty of road, dirt road, dirt rail path, some small single track section and famous mud shoots. (when wet) If the weather is bad it will destroy your bike and that's one reason I don't really do it anymore.
If I ever get a cyclocross bike and plan a serious racing season again, I'll do it.