If you want reliable and still high performance with a wide ratio 6 speed, the KTM 450/525 with the RFS engine is hard to beat. Get a 2004-2007 model, all the issues are sorted on those.
They are higher maintenance than a DR but it's mostly 15 min. oil changes (every 15-20 hours or about 1000-1500kms in dual sport use). The stock intake valves are also a bit soft but if they wear out after a few hundred hours replace them with aftermarket stainless valves and you will get many years of service out of them.
The later years of the WR450F are also decent but due to much closer gearbox ratios they will never be as good as the KTMs as dual sport bikes.