300 mains should be fine. I run the same pipes and similar mods, your elevation in Star City AR is 272ft not to much different from where I live . I run 290's on mine and it works fine. Also the pilots 25 or 27.5 should work, you may not even need to change if thats what the bike came with, most stock banshee's come equiped with either one. To change out your mains just remove the 4 bolts on the bottom of the carbs and change the hex brass jet thats the main jet easy to do, hope this helps.