The age old cell question?
 

What do you guys think of running 10 cells in a lightweight race BL maxx? I think the XL3100, XL3600 or an 8L would be a nice canidate.

I think 32-37 mph is just about as fast as you'd really need to go at the track. These speeds should be achieved with 10 cells along with enough torque.

I have an 9918/8L and will probably try this. Has anyone done this or is it a bad idea?

It's not exactly the situation you mentioned, but at least similar - I've been using the MGM 12012/8L with 8 cells in my brushless MGT. It gets to the low 20s with the stock tranny and 16/52 gearing.
I was actually watching temps and current while playing in my back yard some yesterday morning - the speed control got up to 120F and the motor up to 135F. Ambient temperature was 72F. Running through the grass and putting some resistance on the truck with full throttle, the highest the amp draw went was 66 amps. At full throttle in a straight line it was between 17 and 25 amps.
I'll be putting in the forward-only conversion for the MGT (thanks, Mike) and probably trying a couple smaller spur gears as well.

All that said, I would personally think it's perfectly viable to use the 8L with 8 cells in a racing situation. I would definitely say that you'd want to keep it to the 5 minute races unless you do a lot of experimenting with gearing and try lipo for a 15 minute race.
On paper, it seems that it's always more advantageous to work with more cells, but I can tell you that my setup is working in reality :)

The 8L seems to be drawing way too many amps for 8 cells, and only reaching the low 20s. You may may want to consider running a lehner basic 4200. Not even the xl. Seriously, that's all you would need. You should always run a smaller motor for lower cell counts. By the time you gear the bigger ones high enough to compensate for the low rpms, you're drawing way too many amps. You need volts to get those motors going. I think it was lipomax on the other forums who ran a basic 4200 on 12 cells in an e-maxx and got 44 mph.

with 10 cells you are able to throw out about 900-950 watts. Enough to give your truck a 35 mph topspeed.. But the question is.. For how long? it will draw your batteries really quick! why not go for an XL3100 and 12 cells? the more cells, the more topspeed, the difference between 2 cels is about 120 gram, and you'll get a huge punch of power back.. if you want a truck that is nimble, lightweight, and fast with a normall runtime (about 10-15 minutes) go lipoly.

Though you can built a pretty light truck with 10 cells, the extra 2 cells give you back a large amount of pleasure..