The FAQ said Vex would have an expert evaluate the motors,
and come up with detailed numbers, but all they show is
~100 rpm and 6.5 in-lbs of stall torque.
From an design engineering point of view, ie trying to calculate the desired results before just doing “guess and check”,
it would be helpful to have a torque/speed/current graph, similar to that shown here: http://www.globe-motors.com/15sp_in.pdf
Even better would be to calculate the Power curve and Efficiency curve,
and plot those as well, so we can know what motor speed provides the max power. However, there may be significant differences between motors which would make a standard table misleading, and it would be good to be able to measure this yourself, so you can check the RMA (Real Mechanical Advantage) vs the IMA (Ideal).
A cheap Centronics DVM ($4) from Harbor Freight on sale, as a shunt in the battery line (or PWM cable) will let you measure motor current, in case you are concerned with battery life or motor efficiency.
To find the power curve:
Connect a drum/pulley/wheel to wind up a string lifting a plastic bottle with various amounts of water (weight), and use a stopwatch to measure the time between two heights (=speed). With programming, two limit switches, and an optical shaft encoder, you could probably get more accurate results automatically.
WIth this data, you can measure the effective power output of each motor and motor+gearing combination. At light load and near 100 RPM, there is low power output. At stall condition, there is high torque, but low speed, which is also low power output. Somewhere between will be a maximum power = torque * speed. Once you know that, you can try to design (or guess and check) your robots to run at that motor speed to get the maximum effective power out of the motor.
For best reliability, dont forget to design in some torque margin in case your replacement motor is weaker, or the load heavier, or the gearbox less efficient, than you thought.
A homemade power curve table and graph in your engineering notebook would probably be a plus in notebook competition.