There is a lot of misinformation in this thread regarding wire sizing and understanding of how electricity works. Some basics:

• Power consumers create an amp draw or "pull" from a power source.
• The power source provides voltage or "pressure"
• As the power is drawn from the power source across wires or another conductor, heat is created and voltage is lost.
• The resistance between the power source and power consumer determine how much heat will be created and how much voltage is lost by the time the power gets to the consumer.

Now lets examin the OP's question.

First the battery is rated for 7.4 volts (8.4 charged). This is the available voltage or pressure we're working with. The amperage rating listed is the manufacturer's recommended maximum before damage to the battery occurs. It is worth noting, however, that there is nothing preventing a power consumer or failure (think shorting the + and - leads) from pulling more amperage than the battery is rated for. That would be the job of a fuse or circuit breaker which are not built into batteries. As most know, if you were to short the leads it would not take long for the wires and cells to get very hot and will end in a firey death for the battery if it is allowed to stay shorted. This is where the stories of lipo "explosions" come from.

Next we'll look at the wire size. From the basics we know that the resistance between the battery and ESC is our primary concern. One way to reduce the resistance is to use a numerically smaller (thicker) gauge wire. Another way is to shorten the wire. To scientifically say whether the 12 gauge wire will be a limiting factor the OP would need to measure the resistance of the 12 gauge wire vs the same length 10 gauge wire. He could then do the math and determine how much of a difference there is. This is where the garden hose analogy is often used. The water pressure is the voltage, the hose is the conduit, and the sprinkler is the consumer. A shorter or larger hose will provide more water to the sprinkler with the same pressure. This is what we try to do with large short wires as well. On the flip side there is only so much water the sprinkler will use. There is also a limit to how much power (voltage) an ESC can put to use.

To truly know if the 12 gauge wire is sufficient the OP would have to know how much amperage is being pulled by his ESC while it is in use. The amp draw will vary during use with maximum draw on acceleration from a stop or braking and minimum while at top speed or idle. The simple way to check is to simply feel the wires after a run. Are they too hot to touch? You're probably in the danger zone. Are you melting the solder connections? Something needs attention. Are they simply warm or hot? Then you're in the clear. You could probably gain a fraction of a second in your lap times if you stepped up the wire size or shortened the length but for most the gain won't be noticeable.

I looked briefly but could not find any wire size calculators for the short lengths of wire and voltages that we work with in RC land. Most are aimed at home wiring or car audio wiring.

All that said, the simple answer is that the OP will be fine with 12 gauge wire from the deans connector to the ESC. The amount of extra resistance created for the short length of wire will be minimal. Possibly even less so than the resistance in the deans connector itself. Connectors are where most of the resistance is in a battery to ESC connection. In addition, if the 12 gauge wire was provided by hobbywing then they have already determined that 12 gauge is enough to handle the loads that their ESC will typically use. The 10 gauge from the battery would be like taking a fire hose and connecting it to a garden hose before going to your sprinkler. Could you eliminate the garden hose and run the sprinkler directly from the fire hose? Yep but you likely won't get much more water out of it.