Hi Nick,
I have owned an 07 exc300 for a couple of years now and can't fault it! Pulls like a train, will do the slow tricky stuff and loads of torque, all the qualities of a four stroke and a fair bit lighter and feels very nimble, unless your buying one of the latest fuel injected exc450's, which I believe are only a couple of kilo's heavier.
If you get one with the 11ltr tank you should run as long as most of the fours before you need to refuel, and it's no hassle to chuck a pre measured amount of oil in your tank and topping up with fuel! Generally fuel stops are an opportunity to eat drink and stuff your face with plenty of calories, so not a splash and dash affair.
You can also change the power valve spring easily, Green-mellow, Orange -medium, Red-ballistic, so I'm told. You can also improve the running and fuel economy further by re-jetting and fitting the Suzuki250 REJ needle, loads of info on the UK KTM Forum.
Don't regret selling the CRF450x, which I would say was a little like your current bike. Go for it you won't regret it!