Depends on the coefficient of friction of the wheels to see where the wheels would slip during competition.
I would imagine that the chain would most likely break if your low gear is only going at 2fps, and you had a mechanical failure in which the wheels would get locked.
But in a more realistic view, as in during a match, it depends on how much force requires your wheels to slip in a pushing match. If that force is greater than the breaking strength of the chain, then you just might have a problem. Also, see how much torque is being output out of the gearbox, and taking the pitch diameter of the sprocket into consideration, see if that force is greater than the breaking strength of the chain. That would be in a worst case scenario like that mentioned above if your wheels got locked and your motors would be at stall, giving maximum torque, and maximum damage to motors.
Hope that helps.
Good luck in the coming season.
Also:
When determining the chain length, like Ted said, it would be a good idea to add a little slack and tension it with either an idler, or if you're going with a custom chassis, having a slotted part for the wheel mount so you can tension it. 254 and 968 have done it in beautiful ways. We're experimenting with another way, such as the attached image.