Ok well give some help then. I have heard and read that the bigger 650's are too much for the dirt, and really are only good for desert rallies and stuff, but for super motard that big single would have some nice power. It's no good to me though if I can't keep it up (hahaha) in the woods.
So should I get the 400 then? They are a bit cheaper, lighter and maybe a lot more manageble in the dirt.