I believe that it is 85% rider, 15% bike.

As far as upgrading goes do it because you want to and it is fun, not because of how much faster it will make you. If you are not into racing there is no need to go all out for a bike. The bike you have now is great, until your riding ability is actually hindered by the bike I wouldn't really worry too much about it.

As far as the drivetrain goes, what components do you have now? Also, what fork do you have?