RE: Slow Stick Battery ... Lipo
My EPS 400 is the 5.28:1 gear box and I spin a 12x8 GWS HD(DD) prop. The EPS 400 prop shaft is larger than the 300 and you either can ream out a GWS SF prop or go with the GWS HD props which are sized for the larger shaft and nut. Looks like the shape of the 12x8 HD doesn't draw any more current than the 12x6 SF prop.
You will like the performance of the 3S Lipos much better.
Sierra Gold