you're looking at probably 1 horsepower up top and possibly a little more meat in the mid-range. the main advantage will be weight savings, sound, and it looks cool. for the money you're better off doing suspension or engine work!
Thanks will do:thumbup:MX-Tech are good with WP, Trail Tricks are also par none. Checkout KTMTalk.com
An $800 pipe will have minimal HP gains, most likely less than 1HP gain everywhere. You'd be lucky for one. You'll feel faster cause it will be louder, and it may weigh a couple pounds less.
Look at your gearing, getting some engine mods done, or suspension