aeracer: Well, I don't like to hear that someone is unsatisfied with the perfromance of one of our motors. I have worked at Fantom now for about 3 months. We build all the motors with Red Springs and F315 (767) brushes to keep it simple. I am sure since you race a lot of stock you are putting in the best brushes around.
I really wouldn't recommend going lighter than Red springs for 6 cell stuff. You could use a green on the negative, which will increase your bottom end. Stock motors are too finicky.
Another possibility, believe or not is you could have gotten a bad set of brushes. Brushes are mixed in big batches and then molded into the shape. If for some reason the brush didn't receive a balance of the mixture, then that would severely hinder the performance.
Either way, let me know and I will try to reply. Thanks, and good luck.
Jeff