5S2P 8Ah on a Revo? Where are you going to put it? It is one brick of a battery going at around 2lbs. I guess maybe you're going one 2S and one 3S.

Has he told you what cells he'll be using? All I saw when I followed the links was a bunch of 10C polyrc packs.

Let us know how it turns out. I'm always interested in an economy lipo pack that works well.