Doug, my tests with HRE Reiters and Moorish Camel gunners vs Scottish Noble Pikemen (all 0 exp and armor on flat grassy plain, no weather) show that 2 ranks works best by a decent margin. When I put my cav in 2 line formation, they are able to kill the approaching unit much faster than when I put them in a block formation. I ran each test several times. On average, the Camel gunners could kill about 50 pikemen by the time I had to pull back as they neared my formation. In block formation, they could only kill maybe 20-30 before I had to pull back. I don't recall the numbers for the Reiters but it was similar. Further, I can also confirm that my gunners were far, far less accurate while moving. In summary, 2 line formation seems to elicit the best kill rates.

Cheers!