I also voted for the KLR 650. I keep hearing how it is best for street and fire roads but not real dirt riding. I think that people need to keep in mind the rider skills more than the ride. I have no problems off road, whether it be soft sand, narrow trails, mud, etc. And I'm only a 145 lbs. 5'8" rider. No control problems because of my size. I've heard how the bike will win if you weigh in less than 200 lbs. Not the case. It just depends on your experience, skills, and "balls". I ride everyday on the road and usually find a new off road spot multiple times weekly along with the tried and true spots I've hit with DR's, RM's, and PE's since I was 12. The KLR has been able to keep up with all of my friend's XR's and DR's with no problem. It is not the feeble bike that everyone makes it out to be. Maybe with the stock tires. But that's about it.
The cheapest way to get more out of your stock KLR exhaust is to wrap the header pipe & muffler/spark arrestor with header wrap. I have done this with my '06 KLR 650 with good results. Using header wrap- 1" wide on the header pipe, 2" wide on the muffler/spark arrestor, keeps your exhaust gases hotter, which in turn doesn't slow the exhaust velocity as much as an unwrapped pipe. This procedure actually keeps some of the heat from transferring from the header pipe to the engine's cylinder--where it's less than a half an inch from touching already. It cost me less than $75 for a roll of each- 1" & 2" wide wrap and extra stainless steel hose clamps. I still have enough to re-wrap the pipe and muffler in the event that it starts looking nasty or starts wearing out. I don't see that happening anytime soon though. I was able to reinstall the sheilds on the header pipe and the muffler. @ $75, it beats several hundred for an aftermarket muffler. To help prove the fact that it works, the engine actually runs a little too lean with just this modification alone. Any other mods to the airbox and such will only aggravate the lean mixture further. It's not a new idea. Auto drag racers have been doing this for decades. I just haven't heard anyone with this idea for the KLR. Hope this helps.