I'm looking for a bike that will lug nicely through the single track scream up the logging roads and be a hoot on the open sand river rides.
To me that sentence says it all. If you want to lug, go with the 300. It will be much happier lugging around at low speeds than a 250. I've got a 300, and I just came off a YZ250 that had a flywheel weight on it. While the YZ would lug, it has nothing on a new 300. A 300 will pull you along at walking speeds over stuff that would be hard to walk. My 2 cents for what they're worth.