I think that the guys who are suggesting the Yamaha product are hitting the nail on the head.
But instead of a WR250. You might want to check into weather or not you can get a WR450 plated.
Well you seem strong enough to handle a 450. You want the speed and the highway miles. Thumpers last longer if you don't have to ride them full throttle. And if you don't want the full hit of a 450 you can get a device called a throttle cam. This device slows down the throttle response at the low end and makes it a little faster near full throttle. The stock throttle is pretty linear all the way.
The KTM and 09 and newer Husaberg and Husky product are all really good product. Some are might be better off road. But none are quite as maintenance free as the WR product.
Good luck to you in what ever you choose.
Why would I want to do that??