My advice to you is to get the CR 250. The 450 is ok if you get your jollies out of working on a 4 stroke and the expense of them when something does go wrong. They are also heavier and pound for pound the two stroke will always have the power to weight ratio. I know the 450 is only like 12 pounds heavier than the 250,but most 4 strokes like that KTM everyone on here is talking about, and you sure don't want that for where you ride If I remember correct you ride in the flat or sand with a lot of speed behind your riding.If you want a bike like a 620 or 520 4 stroke, you should really look into buying a good used CR500, you can't beat the power of those bikes and there isn't a 4 stroke made to keep p with it. The 2 stroke is also very easy to get the power out of and easy and cheap to fix/work on. I wouldn't hit a bull in the ass with a 4 stroke dirt bike,if I'm getting a dirtbike, it's gonna flat haul ass from the bottom to the top. I've played the 4 stroke game before and you couldn't run fast enough to stick me with another one. I know they have came a long way with the new 4 stroke bikes but seeing as how you got a banshee and quit messing with your X, I think the same would apply to this, you would be much better suited with the 250.
ATC350X,ATC70,1991 RM 250,XR500,TM400,TS400,Foreman400 4X4,Polaris 425 Magnum,ATC 90, 1982 175,1973 Honda Trail 90,1980 CR80,1981 CR80,