gearing tip for 8xl ?

[speedy]

Hi !

I need a tip on what pinion to buy for a 8xl feigao motor used in a inferno 7.5 sports buggy with stocj spur and 4s lipo ? I'd like a topspeed of 40mph if possible :)
I'd like to use a bk warrior o mgm esc but witch one ? for maximum 300 $ o and how big lipopacks do i need for 20-30min runtime on a track ?