It depends on your current draw rather than voltage - the easy rule of thumb is to use the same size as what the bigger of the ESC or battery you are using has fitted as both of those items are specified for the maximum rated output and if your cables are long you want to go with larger wire to minimise losses.
These wires are just amazing. These are very flexible. Keep them in zip pouch with some powder to avoid getting silicone hard because of moisture. If you order 5 meters, you will get full 5 meters in length. No cutting or splitting. I give 5 stars to it for quality.