on dual 3S lipos ran in series to make 6S (22.2V), probably the best bang for the buck ESC in my opinion as it has a 1 year warranty and the price is cheap relative to other places is this one:
Castle Creations 1/5 Mamba XL 34V Extreme VS2
http://www3.towerhobbies.com/cgi-bin...&I=LXBRBB&P=ML
Can handle 8S and has datalogging capabilities. Give it a read on castles site.
Now, it is backordered right now, not surprised at that price. But if you need waterproof, the Mamba Monster 2 would be my next choice.
http://www3.towerhobbies.com/cgi-bin...&I=LXDAXB&P=ML
As for motors, if you can find it, the 1518 sized motor will give you the best of both worlds as it can handle 4S and 6S, is a longer can than the 1515 2200 and will offer more torque and run cooler. They come up used all the time.
Or, find a 1520 1600Kv for 6S running (4S it can do, but you are at a really low kv so gearing comes into play). that is what I use. Even more torque, runs cold and I am using it on a 1/5 scale conversion of the Savage Flux.
When you mate the right Kv motor with the proper voltage, you keep things running cool and have better gearing options. the 1515 Castle or similar HPI version can do the job especially in just an XL length setup, you just have to watch your gearing more.