I second the ECO design.
I have raced this design ( Forrester hull) with 2000Mah cells on a 19 turn for 4 min. enduro
Lots of juice left in a 2400 pack after the race is over.
I would go brushless for the extra speed, single motor, and most likely 7 cell or 2X LiPo.
If you can keep the amp draw around 20, a 4000 Mah pack should just make 10 min. May be tough to do on anything less though.
Peter R.
www.climatemodels.com