From what i have seen in oval racing..(its what i do) .. the Cobalts dont work as well on larger tracks.. on smaller carpet tracks there awesome... But on the big outdorr asphalt tracks they are lacking.... i would assume, they may be the same on larger road course tracks....
As for the xxx brush.. there awesome... i use them in stock motors, and 19 turns as well.. they are a very good brush for the money...