picking a new bike is hard.

do they have demo days by you, anyone at the track have either of the bikes youre interested in?  the yz250f and 350sxf are both killer bikes.  Im a vet rider and learned suspension is more important to me then motor, so Im currently on yamaha from a ktm(6 years) and love it.  with all the mapping, tuning mods etc its easy to get a bike to have the kind of power you like.  but starting with factory kyb which youre already used to an like i assume(yz250) will be a better starting point in my opinion.  but that 350sxf with 2k in suspension conversion is a killller bike

I'm at a loss myself, 250 4 stroke wears me out, i want a 350 but hate air forks, every time i ride a 450 i get hurt.... 

350 with spring conversion.

Old and slow here. I need a bike which has most comfortable and stable chassis with not too much power. Been on an Austrian 2stroke for years but have been trying different bikes lately to seek for a next option...

Yamaha 125-450 will be the choice, but can't decide which one. Maybe too lazy for 125. 450 has too much power. So most probably either one of 250s. 

Kx450… drill some holes in the airbox if it’s too mild power wise, but the suspension chassis and engine together are amazing with minimal set up.