The stock battery for all rtr's is gunna be dooky so be ready to ditch that. The C rating is about constant discharge levels so yes it can give extra performance at a price (That's about the simplest explanation, there is a TON more to it but i would be worn out if i typed that much, also there is a lot of theory about the subject) Be warned that too much discharge or not enough can be a bad thing. I would go for the high MAH battery to give some nice long run times. If you were racing then worry about the crazy batteries, but just for fun the 20c 4000mah should make you pretty happy. Read up on that boats electric system and see what it's limits are. Keep in mind that the limits listed are the highest you can run for a few min with out catastrophic failure. If a vehicle says 6s lipo limit then i would run a 4s to make sure my hardware lasted but was still fun and fast. Stay in the middle of the stated limits and you should have a good running boat. If anyone wants to chime in feel free, i'm sure i missed things.