We've had a little chat about it here
- seems that a 4-cell car with a 10/11 turn mod is similar in speed to a 6-cell car with a stock. Handling is better with the lighter car.
Seems the same deal as with 12th - the 4-cell cars are smoother with a bit more top end, and handle better. The 6-cell stock cars are more brutal and handling suffers from the extra weight.
Personally, I think 4 cell has potential as a racing class - my only real concern is low voltage to the receiver (unless you use an rx pack - and who wants the hassle of recharging one of them all the time?).
It won't catch on in the mainstream though, 6-cell is too established, and it's what beginners buy. 12th scale managed to handle the change because it was already a specialist class - 1/10th touring isn't.