How many tracks to use? None, ever... right?

How many arms to use? More than one because 1 arm would have to be a piston and it's too slow. Less than 5 because max rate on silver is achievable with 4 and I'm keeping proliferation out of this. Between 2, 3 and 4 arms I don't really know, so I tried different ones but couldn't find anything that makes 3 arms work at rate 12 nor 2 arms at rate 18 which would be the target for sub 220.