Mods will help, but the rider also helps alot with the mods I have I can easily beat 300ex's.

 

The mojave engine has more potential thanks to 4 valves. You need to help it flow more air and fuel thru those extra valves. Get a good exhaust, I have had supertrapp and white bro on my mojave and the white bro was superior. Switch to a 13 tooth front sproket as thats pretty cheap, get some good sticky tires and let it get more air, I use twin air as it filters dirt better than K&N, but If your after horsepower to win I'd use a fresh K&N (they are never as good-as-new after cleaning) or a very thin foam filter. You can also cut the snorkel off or drill large holes in it but there again it increases potential to suck dirt. Dont waste money on a jet kit, simply buy a few jets and youll save some money. The above mentioned items will beat a 300, but you mentioned cams and not knowing anything about the competitions grind, you may also have to add some cams, you may first try a good valve job and a little light porting work. If you add the white bro pipe you will probably want to eliminate the factory rev limit.

 

The 300ex has 4 valves too. It's just the mojave is double overhead cam and the ex is single overhead cam.

 

The dual-overhead cams help the Mojave rev faster compared to a single cam. I have ridden a 300ex and a 400ex and I can tell you I will never go back to a single cam because they rev so much slower, that it the 300 and 400's downfall. There is no upgrade that can replace dual overhead cams.

 

It is not the number of cams as much as the number of valves the cam opens and closes. The more valves (which are smaller) the lighter the load is on the engine, which makes it rev higher.