well, from what i gather, i rode the entire summer on my stock 03 at a pro track(englishtown, NJ) and it beat the crap out of me....you gotta change the tires for sure...theres no getting around that...a good set of pipes...and if you have the money shocks and a-arms....personally, for next season, i plan on getting my swingarm cut, some new rubber, and if i have the money which i doubt, some pipes....but i will be racing so we'll see what happens then....
i'd say the stock rear tires are the biggest problem....i mean...i'd be going up to jumps 3rd gear almost pinned, and feel the rear end spin all the way up the face of the jump....i had no traction....around turns i was spinning out, and doubles were always a no no because i never had enough speed going into them or i'd just spin out....
Also i'd say gear it down a tooth...get some nerfs and a kill switch and go racin'