Have you considered joining the brushless revolution? More bang for your buck and you can then modify speed controllers.
Hmm... why not? :P I understand brushless motors can be fiddly though although I guess that comes down the choice of speed controller? The change in brushing will mean a change in motors mind... will need to go on the hunt for something suitable that I can work with though I have something in mind that'll work with the design of Kaizen.