The Tour of Gila is hardly "one of the hardest mountain bike races" though no mountain bike race is easy. The trail had to be rather smooth for an old stump jumper to get a racer in. I used unsuspended mountain bikes and now use cross bikes but they can shake your eyeballs out of your head.
I presently have a Redline Conquest with disk brakes that's really great but the best flat ground and mild climbing bike I've ever ridden is my Ridley Xbow. If I could get the rim brakes to work well enough on the Ridley I'd pass off the Redline which is also a great bike. But I'm filled up in the garage area.