Dunland - In theory you are correct...in practice you can never get the exact same wattage output on 4 cells that you can with 6 cells no matter how wild the motors are or how high you gear it.
Tim - There is no difference in carpet wear due to tires. Scotty Ernst the most respected guy in our indurstry (other than Mike Reedy) and a long time carpet track owner has said this several time before. As have the owners of Stockton R/C Raceway, Rain City Raceway and a lot more.