If you are thinking of a dirt-only (non-street legal) machine, there's nothing at all wrong with a 250-class bike. They feel like a mountain bike on trails compared to even my 450. Or, along the same lines, you could go 2-stroke and find a good KTM 300. Best of both worlds and easy/cheap to maintain. Perfect for the dez and hills. Markus knows...

I do know. I was really wary about buying the two smoler, but it is really an awesome machine. I have a buddy that I ride with all the time who made fun of my KTM constantly (damn Honda riders

). Last week he showed up at the trails with a 2008 KTM 300 XCW-E.

That's a great trip for something like the 640 Adventure. With Krismark being pregnant and all, I don't think I'll be doing any more trips like that anytime soon. That's all good, because ever since I purchased the 300, the 640 has only left the garage once for about 10 miles to see if it still runs (and it's been about 9 months).
If you are really looking for something for trails that you are going to load up and take to a trail head, don't dismiss the KTM 300 two stroke. They really are good machines.