[Al Skierkiewicz]

Here is the way I interpret this rule...
<R48> The ES-18-12 Battery, the Main 120 Amp Circuit Breaker, and the IFI CB/Distribution panel must be connected as shown in the diagram. The ES-18-12 Battery must use the Anderson Connector and the copper SLU-70 lugs provided in the Terminal Supply Bag. The Battery terminals and the SLU-70 lugs must be insulated with shrink tubing and/or electrical tape. You may use additional lengths of #6 red and #6 black wire to reach the panel as needed to make the above connections. The circuit breaker must be readily accessible for inspection and testing at each competition event.

The #6 and the red Anderson connector provided must be used. Elsewhere in the rules, wire minimum sizes are specified, but no additional reference is made to #6. Simple answer is use what is provided. The tradeoff for lower resistance/higher weight is not significant to warrant the change. (The wire length should be too short to matter.)
I would like to know what "high quality" #6 wire is?