the cheapest easiest and one of the most noticable things to do would be to change your gearing. you could go down one or two teeth on the countershaft and up 3 or so teeth on the rear. for every tooth you go down on the front it is about equal to going up 3 in the rear. so a -1 drop on the countershaft and +3 on the rear sprocket will give you about a +6 in gearing. you will have a noticeable faster acceleration and you will hit your shift points faster, but probably not a bad thing for racing. you will however loose some top end, but probably on 5 mph or so.
next thing is that KTM motor is a bitchin' motor. when comparison test between KTM's 525 XC and Polaris Outlaw 525 were ran, the KTM was 2-3 quad lenghs faster at least, even though both machines have the same engine! the airbox and exhaust on the outlaw was designed by polaris and is restrictive. get an aftermarket exhaust. good companies too compary availbility and prices are: FMF, Two Brother, Leo Vince) I will work on finding you links to specific exhaust that will work but those three are my favorite brands.
air filter wise, you should be able to get something like a K&N which will flow a little more air, and you can punch small holes around you airbox.....like 6 1/4" holes to start. this will get more air in, which will poor more fuel in too, and with the aftermarket exhaust you can get it back out.
of course all of this will mean you will have to play with the jetting and keep fine tuning it until it runs right. if you are running on stock jetting right now, i can almost bet you are running too lean and that is hurting your performance too. they come jetted pretty lean from the factory.
