I certainly see subtle yet distinct differences in on track performance, most noticeable in the ability of a stock motor to clear large jumps. The key is not the max amp draw with a hot modified or a speed run car, but rather maintaining voltage under the moderate load of a stock motor.

Here is some independent data, just one example of many sources that suggest lipos differ in their performance, even at relatively mild loads:

http://www.teamvirusracing.com/node/750