Running in a Revo, you're probably going to want a 5S2P setup with the A123s. They are very nice batteries. I got the opportunity to play with some and I was impressed. They really do charge in 15 minutes too.

The downside is that they are heavy and bulky. A 5S2P pack is going to weigh 700 grams (that's about 1.5lbs) for a 4600mAh pack. With a Neu 1515/1Y, I'd guess that it would get you about 15 to 20 minutes of runtime.

The other downside is that the fast charge rate is kind of misleading. It can be easily done with the commercially available A123 packs and the accompanying charger, but for a 5S2P pack, you'll need a charger capable of charging at the 3 to 4C rate required to get the 15 minute charge time.

I have a ThunderPower 1010C and it's capable of charging a 5S pack at 10A. It took me just under half an hour to charge a 5S2P pack. Of course, you could just build two 5S packs and run them in series and then have two chargers, then that would get you to 15 minutes of charge time.

I really like the A123s, but I don't use them for racing. They knock my weight distribution all out of whack and to be able to run a 30 minute main, I'd need 3lbs worth of battery.

I'd go for 4S lipo. If you are running two packs, you could go with the trak powers.