While this is very old I'll give you my conclusions based on actual flights. I have tried 5S, 5000mah, 20C, 6S 4500mah 25, 30 and 40C packs. The 6S 4500mah 40C packs work much better than the 25C and the battery capacity upon landing has gone from 18% left (25C) to 35% left (40C). 5S worked fine, but really not for competition in Masters Class. 6S much better - and going from 25C to 40C with the same 4500mah battery gives me better overhead having 35% left. Same throttle curve, same style of flying - but I may have changed the throttle curve - down a bit at 50%, 70%, 85% but don't recall for sure. I'm on my 3rd season with the 40C batteries, where the 20C were having trouble after 2 seasons of flying. No signs of battery swelling and all packs were Zippy Compact cells. Weight between the 5000's and the 4500's is close as the 5000's were 20C and the 4500's are 40C. The 6S, 4500mah, 40C's work great and really tune my flying style with the plane / weight and throttle curve and prop.