We opt-ed to use the FIRST gear boxes. (Team 292) We powered each side with 1 drill and 1 chalupa. (Chalupa = CIM) Ran that through the FIRST gearbox to a sprocket. From there we reduced it even further to the wheels. A lot of our power and traction came from our 8" pnuematic wheels.
I'm not saying we used them the best, but a lot of teams had a very hard time pushing us around ('cept for 25).
One of my favorite matches was during the finals in Chicago. Huskies had their legs planted in the grid, we came up and pushed them off the top. 45 gave us a slight nudge to help at the end, but we had them mostly off by that point.
Here is the link to the match on SOAP
http://www.soap108.com/2003/movies/il/il_fm1.asf