If you race, with a 4S lipo on that high of a KV motor it will be too much. I don't think you can gear down low enough to make a difference. 3S will get you were you want to be.

The zippy packs are great but make sure you velcro it to the bottom of the chassis as well as using your straps because they tend to crush easy. You do not want it to move in the tray at all.