How can a set of jets be either good or not good for road (or track)?

The "arguement" for not buying the jetkit if you've got a near stock motor is that you won't use 95% of it and you could get the exact same net result with a set of mains.
So that's spending about $10 rather than several hundred.

This is Steve's mc18 dyno graph from quite a while back.
That's just wiresplice, race pipes, modded airbox and a different main jet.
_________________
Please do not PM me technical questions, if you can't find it on the Forum start a thread