1999 arctic cat 300 4x4 upgrades

I have a 1999 artic cat 300 4x4 and was wondering how i could get some more speed out of it, i havent found any pipes will fit, i do have a uni air filter, it works great in 4x4 for bushwackin. but not much on the speed and touque department, except in low it has good power thanks! Also is their anything that i can do to make it more mud friendly? Larger Tires? Lift kit? thats what i really bought this machine for mudding and deep water, is thier any way to build or buy gaurds for the front diff so when stuff hits it it dosnt break somthing.

On some of the later models they were doing a stock muffler mod by adding another exhaust port to the stock muffler. Here is an example of a moded 300.

"for the muffler mod, i cut off both ends, drilled some 3/8" holes in the first baffle, completely removed the rear baffle and installed a larger exhaust outlet."

[ame=http://www.youtube.com/watch?v=zqESLN2MrYU]YouTube - Arctic Cat 300 muffler mod[/ame]