Here's our setup:
BaneBot 4 7/8" wheels on top and bottom, each independently powered by an RS-550 with a 7:1 gear reduction.
We measured the current into the motors when it was running at "full speed" to be about 7A each. Plug that into Ether's
Motor Calculator, and we see that the speed of the motors is 18007 RPM. That gives us a speed of 2572 RPM for our shooter wheels, which is quite sufficient (we can hit the center of the top backboard from midfield, when running at "full speed").
Now, given that we're using smaller wheels than you, you should take that difference into account - you need about 5/8 the speed we have to get the ball to go the same distance - or about an 11:1 gear reduction.