Dowop, there's a great thread floating around somewhere about choosing between 17or 18. The ONLY thing it may hinder at al is the low end 1st gear accelleration. Then the only difference is you just shift at different speeds. If anything, it HELPS on-road accelleration because you can hang out in 3rd gear longer and just punch it around people. But go check out the threat, lots of posts, lots of opinions, and hey, it's your bike!!
