Ezrun 150A can handle 6S. So can the Mamba Monster, and the Tekin RX8. Your 7700 motor will die the moment you run on 6s. I advise you get a lower kv motor and try 6S. What gearing are you on (spur and pinion).
Losi 8ight-E 2.0, LRP Shark, Xray M18T custom extended, Traxxas VXL Revo