What is the torque output of the gear boxes provided with the kit using two small CIM motors on each one, as well as the stall torque.
It depends on the wheels you’re using. But if you do the 8" standard wheels that come in the kit, if my math is correct, you should have a top speed of 10.9 fps using the free speed of 5310 rpm.
(5310rpm * 14/50 * 14/50 * 21/28 * 8in/12in * 22/7[pi])/60 seconds
For torque, you should have 29 ft-lb using 2 cim motors with the stall torque of 343.4 oz-in.
(2motors * 343.4oz-in * 50/14 * 50/14 * 28/21 * [5.208 * 0.001]{to convert to ft-lb})/(8in/12in * 22/7[pi])
I hope that helps.
If my math is wrong tell me, because this is the way that I use to calculate the fps and torque for my gearbox designs.
http://www.arkorobotics.com/images/speed.jpg
This might help. 
It’s in the PDF, you can find a good 10 pages worth of gearbox stuff. I recommened the combined pdf.
All the answers to your questions are in the 2006 transmission manual. The gearbox output torque curve for a two motor drive is in the appendix of the manual located on the IFI website.
Located on this page:
http://www.ifirobotics.com/kitbot.shtml
Here is a direct link to the PDF:
http://www.ifirobotics.com/docs/2006-first-transmission-manual-rev-d.pdf