I have the 04 exc200. It has and is known for having very long legs. I have no problems with 450's in straights (unless your talking Hare&hound miles long straights that is). They tend to briefly catch up to me but I always seem to get back by before the end of the straight.
I'm also in Oregon and am racing the OMRA GP & XC Series and despite the bikes age, it's very competitive. I haven't been on the bike in the dunes yet but it's been great everywhere from the rainforest of Tillamook to the Oregon desert (Chinahat / Millican).
If your coming from a 125 2-stroke, you'll have to get used to lugging it in the woods and mud. It puts the power down a lot quicker then you would expect.
I'm 6'2" & 192lbs so any bike is going to like you a lot better then it likes me.