Buy the '07.
The 865 motor, if I'm not misinformed, is tuned more for torque. The 790 motor has hotter cams, and has a better top-end hit.
I'd bank the extra $1200, ride the heck out of the thing, and when you're bored with it (like
that's going to happen) spend the $1200 on a big-bore kit (and have plenty of change left over).
