Mike is one of the best people to ask for help by FAR. But on these forums there is a lot of others that can help. You might have placed your post in another spot but some one will find it. To answer your question about a pinion and motor we need more information about your set up. What batteries do you plan on running? What ESC will you be using? That kind of thing. Here is a good link from another great and knowledgable member named BrianG. He put some good information that could help you out.
http://scriptasylum.com/rc_speed/index.html
Try putting another post in the Brushless catagory with more of your info setup. Hope this helps.