For arguments sake, your aim to is to make a G36c that fires 25rps at 350fps. Here are the numbers :
E1 G36c - 150$ - ?? RPS (not 25rps though, I own one, more around 18 rps) 350fps
KWA G36c - 245$ - 20 RPS - rated at 360fps acccording to retail sites
All you would have to do to the KWA is put a better battery in there and you ahve a G36c that shoots 360 fps at 25 rps, reliably. The E1 is a venture that will be more trouble, cost, hair pulling, etc etc. Switching to LiPo won't be the difference in that cost. Its the BETTER of the two choices.