...so maybe I'm wrong...
The Busa is smooth and tractable but still big and heavy...I learned a lot of things on smaller bikes that makes me better on big ones that would have been vary hard, if not fatle, to discover on a larger one...you may be thinking with your pride and heart...this is how most of us buy our bikes...I realy cannot explain how it is I have a Busa myself, let alone have a Turbo on order...
...but be advised, that while I have no track time to speak of and will never have a racing sponcer, I smoke a couple of ex national motocross racers in the street, in the twisties, anyway...that is what scares me about your situation...we have a guy from the North End we like a bit who has already crashed his Busa because of inexperience...he defeats R1s and all on high speed runs on the highway but does not us the front brakes!?
This is the **** that happens to guys with a lot of natural talent that get in over thier heads... they don't have a chance to figure it out before the laws of physics arrange a demonstration...the dirt and an Ultra Sport bike are very different...dispite the need for a stong dirt backgound to have a chance at a GP ride, even those dudes rarely start out on the 500s...did you get a CR500 for your first dirt bike? Would you recomend this to a friend?
So I will have to stand by my position....you can go to the shools, but they will not keep ypu from crashing the first time you boil up over a hill and around a bend at 90mph and spot parked trucks in half your lane and oncoming traffic that causes you to hammer the rear brake out of some missguided left over braking reflex (don't ask)...
That said, whatever bike you get, got to the schools, and especaily go to a Motorcycle Safty Foundation Advanced Rider's Course, as lowly as it my seem...it will be the best $50 spent on your riding...
I'm not saying to get a 250 Ninja, althoug it is a goodbike, but i thiknk even a 600 would be less than Ideal...considering that you have been spioled to some degree by the Busa, however, I would go out on a limb and recomend a new ZX6, R6, or CBR 600 if you got the coin and need the flash...but be prepared to deal with the expense or even a minor tip-over...I'd go with somthing a bit knarly to start with, as it it likely to get knarled up a bit rather quickly...don't worry, there will still be Busas and upgrades and all in a coulpe of years...It would be nice if you were, too...
I truly believe you will go faster and have more fun on a smaller, lighter bike than the Busa in any kind of demanding riding situation...this has all been pretty well documented at this point...