Anything above 25C continuous would be enough. However, many people have switched to 35C or 40C continuous discharge rates, as the voltage drop under load is not as large as lower C cells, therefore the cells maintain a higher voltage and so the motor can utilise more of its rpm/V (kV).
I personally run a Thunderpower 40C Lipo in my CAT, but I'd have those Trakpower Dark Series Mark has mentioned 'cos they're really nice! 35C or 40C discharge dpending on which you choose, 5C charge rates, excellent life time. Yep, I'd have them. They're about the same price as the LRP/Nosram packs, but will be more accurately rated and closer to their actual specs.
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