Efficient Cobblestone Generation

I am designing an automatic lava maker (cinder dust needs to be provided, but the rest is fully automatic), and I was testing to see how many mechanical drills would be needed to keep one 256-RPM mixer stocked with cobblestone at all times. As part of these tests, I experimented with different speeds for the drills, and I encountered some interesting results that are in the table below

Drill Speed

As I discovered in my testing, any drill operating at 76 RPM or higher will provide 40 cobblestone every minute. There is obviously something strange happening at 64 RPM as it's producing less cobblestone than the 32 RPM drill. That's because between 51 and 75 RPM, the stone generator turns into a cobblestone or stone/cobblestone-combo generator. When that happens, not only do the drills operate more slowly (cobblestone takes longer to break than stone), much of what the drill breaks is lost as well. At even slower speeds, the efficiency is probably even higher as the time to generate the stone becomes less and less a factor, but you obviously need more drills to produce a lot of cobble.

Efficiency Conclusions: I know Create is for many, perhaps most more about fun than efficiency, but I thought I'd throw this out anyway. If you want to squeeze the absolute most out of your power while still producing cobble at a reasonable rate, run your drills at 76 RPM and make sure you're generating stone...anything at that speed or higher works exactly the same. If you're only interested in power consumption, the lower speeds are better with 1 RPM probably providing the best returns per SU although I didn't test below 16 RPM. If you want the most inefficient cobblestone generator and most lag possible, set your drills at 75 RPM. Anything between 67 and 75 RPM will ensure that none of the cobble actually ends up on the belt but instead is spat out on the ground.