All you need is one pack per car. Throw it right back on the charger after your heat, and it should be good to go by the time the same heat is up. The C ratings are mostly marketing. 40C rated packs are great for anything except modified. The Gens Ace are great bang for the buck, when you can find them in stock.
For mere mortals, capacity is more important than C rating, especially for stock classes. As an example, in stock TC, I use about 2000mAh in 6 minutes, for an average current draw of 20A. Given that a 40C 5000mAh battery is supposed to be able to provide a continuous discharge rate of 200A, it's not a stretch to realize that the C rating really doesn't matter. The burst current rating of most Lipo batteries are usually 2x the continuous rating, or in this case 400A. Again, way more than required for stock. Also, 12 gauge wire is only rated to carry 60A, as are Deans connectors.
Get the brand you prefer if you don't want to risk the no-name brand.
*** The Gate - Celebrating 7 years at the same location ***
The difference between genius and stupidity is that genius has its limits. - Albert Einstein
Understeer is when you hit the wall with the front of the car and oversteer is when you hit the wall with the rear of the car