Which Neu motor are you running on that 5S. 5S is pretty high voltage for a truggy and if you are running a reasonable motor, such as a 1515/2.5d or similar, you don't need the best battery money can buy. After all, one of the major reasons for going with a 5S setup in a truggy is to run a more efficient system that draws less current.

I'm running a truerc 10C 5S2P 8Ah pack in my 13lb truggy with an 8XL and the pack hardly gets warm. The truerc pack was under $200 shipped. You really need to give us an idea of what you current requirements are going to be.

If you simply want the best that money can buy, then flightpower's packs with the highest C rating will be it.