Thats a loaded question
100 answers will bring 100 opinions. YES better brushes will bring a little more power. Lining up your brush hoods properly will make the biggest difference in how your motor runs. If they are already right, then I would say "Race" brushes are probably the next way to imporve performance. I use Reedy 767 brushes with a 5/64 hole in the center. The hole does not gain torque or RPM, for me it seems to help keep the brush surface much cleaner so they work better for a longer time. Putnam has some real good brushes in 3 different amounts of silver. Trinity 4499s are good too. I THINK those are too hard on the comm. If you want to run "High Performance" brushes, you should have a com lathe. It will help you get the performance out of your motor. You are supposed to true the com before replacing the brushes anyhow. If you can't try to get some one to do it for you or your hobby shop.
David Root