I also had speed woes with my blackfoot extreme, so i shoved a 17t motor and a 7 cell battery in it (!)
This gave more satisfying speeds, but has resulted in a lot of broken parts, including major chassis damage (expensive to repair [:'(]).
imho the blackfoot extreme was never meant to go fast, it has pitifully small suspension travel and doesn't crash very well at high speeds. That said, putting a brushless motor in one would be a great laugh and i'd love to see a video []