[BGiraud]

True. In theory the traction should not change. In practice, more contact patch wil make a small difference. We staged a tug of war between our twins. Both at 120 lbs. One had 12 wheels and the other had 6. It was a tie. Theory wins!!! But, when we drove them there was a noticable difference. The one with 12 wheels was more controllable. You could see it and the drivers could feel it. Both of our drivers requested the 12 wheel configuration for competition, but the 6 wheels for fun. The six wheel set-up turned faster and a bit more uncontrolably. Other tests proved that acceleration and turning were simillar, but stopping (sideways slide) was much better with 12 wheels.
Since we came in under weight we decided to keep the 12 wheels. In the end we all agreed that they look cooler than six. If weight was an issue then we would have dropped it to six wheels.
Verdict - There is definately something to be gained by increasing your contact patch. It might give you a slight edge, but it isn't a game breaker. I have found that this holds true for rubber on carpet in previous years as well, but that is another story. One that many theorists would like to argue I am sure.