Not just gear ratios. You need to know how you'll be using your robot. If it's acceleration Have a target distance you want to travel to (ie. 13.5 ft), and optimize the acceleration to reach that distance in as little time possible. Remember, the higher the gear reduction, the more the effects of acceleration are noticeable, but that also means you'll be moving slower. You need to find the happy medium where your speed is high enough to utilize the high acceleration to get to your target distance as quickly as possible, but your speed has to be low enough to make the acceleration effects noticeable. You can play around with numbers in the JVN design calc and JVN's acceleration spreadsheet, and see what works out best. A good thing to do is set a speed for a 4 CIM drive, then change the number of motors to 6 CIMs, and see how the time to distance changes. If it's significant, it's worth using. If it's insignificant, the extra motors aren't helping. Of course results may vary, but from some quick testing I did over the past year I've found that for most usable speeds in FRC at common target distances, the average amount of time shaved off from travel time between point A and point B is no more than a quarter second at most, which I'd consider not being worth it. That being said, this was assuming a total robot weight of ~110 lbs. Lighter robots will feel the effects of acceleration a lot more.

Another thing to optimize for in 6 CIM drives is torque, especially if using a PTO. Torque is straightforward - the greater the reduction, the more torque there is. However it is still something to optimize for if you are using PTO.

Like I said - it is all dependent on how your team sees things and the data you get from testing and doing your own math. My experiences over the past year have made me come to believe that unless you are using a PTO, a 4 CIM transmission will get the job done just as well, without the danger of tripping the main breaker and without the extra 5.64 lbs of the two other CIMs. While these are my experiences, the best way to make a decision is to go out and test things out for yourself.