Mark,
the most common setup is 10.5, orion 3800's 30 c batteries. Pleanty of runtime, and just as fast as Kyle...
I played with 78/26 on saturday, full boost on my speedo and had plenty in the end.
My slash runs a 6 cell batt, and is just as easy to drive, and just as fast as on the track. More power doesnt mean faster, and plus it would be a few dollars cheaper for the Slash entries to buy a 6 Cell pack, insted of a 7 cell pack. Just my 2 cents.
Also 6 cell would be easier to drive for all of the beginners that run slash. Many people alwayls like to over power their racecars whatever class they may be participating in. I think make it a little slower, turnining out to be more entertaining, and more controlled at the same time. Slow is fast.