My bike is a 2008 rockhopper comp with the original wheels on it. I'm looking at upgrading the wheels to use for cross country riding/racing. I'd like to keep the price around 300$. I'm not afraid to build my own wheels if it will end up being better in the long run.

As for parts:
The only thing that I've decided on is the Mavic XC 717 Disc rims.
I've heard alot of talk about going XT/XC 717, is that my best option?

I just need help choosing, buying, and building my new wheels. All help is greatly appreciated.