I dunno, I been riding dirt most of my life since early childhood, and almost always on a 250 (2 stroke back in the day, later a CRF250R), but after riding my buddy's 500EXC, I'm totally in love with that bike--and I think it's as tame as you want it to be, yet has more torque than a 250 and for the money, it's not that much (comparatively).
A new Honda CRF450X costs $8440, isn't sold as street-legal, and isn't as good of a bike...