I also don't understand what the 350 is supposed to do. Isn't the only reason why four strokes are so "great" the fact that they can have double displacement?. Why not use this advantage if it's practically the only one you have? If a 350 sxf, or whatever, is as good as any 450, they say, than so are 250 two strokes. So basically if you buy a 350 four stroke, you buy a 250 two stroke that's overly complicated and has unnecessary moving bits inside the engine that go very fast and tend to break often.
the fact they rev out to something like 13500rpm
...and other things they did to the engine to make it go almost like a 450 are amazing in terms of engineering, but nothing more than a massive headache for anyone owning a bike like this other than the factory teams. I think if I had to go four stroke I would still buy a 450 F because I believe it will be more reliable somewhat. If the power is to much, ride a 250 F. And if you can think for yourself and know what's best, just get a two stroke, forget about everything and just enjoy racing. That's my opinion.