It would smoke most 650's. And it handles better that any sx, 750 or 650.
I had a 650sx with a coffman's pipe, 44mm carb, 9/17 prop and a milled head. There was a guy on sand lake in the irish hills that had one that I would ride with. On take off he would usually pull ahead, I barely had him on top speed.
I got sick of sit-downs about 6 years ago. After learning how to ride a stand-up and getting good at it, I could care less about anything with a seat. You just get bored too easily.
If you put it on eBay, You'd get a grand, easily.