Four strokes vs. two strokes
Take it from me, the 4 strokes are great, but when it comes to rebuild time, they cost big $$$$. I don't know where you live, or the off-road registration rules, but you can't beat a two stroke for power, ease of maintenance, and cheap parts. Take for example the cost of doing a top end on a newer 450 4 stroke (Honda, Yamaha, Kawasaki)that runs in excess of $1,800.00. Doing a top end on a 250 two strokes will run you about $300.00 (if you do it yourself). And god forbid if the 4 strokes rod is shot, or is bent, then the cost jumps up to around three grand for a complete rebuild.
You can pick up a 5 year old CR, YZ or KX for peanuts, and you'll be rewarded with a bike that reliable and fast enought to blow all those new four strikers right into the weeds. Here's a shot of me wringing out a project CRF230 for off-road.com last year. Neat handling, but needs more motor. Like riding a big SL100.
Good luck on your search.