Crusher norm for feathers. No clue
Ram power ain't the main thing. Pressure on the tip is what counts, combined with the shape of the tip.

Also, stroke and speed have their place.

The 20mm rams, what stroke are those? If the stroke is longer than 40, the forces impared in robot combat will bend the rods.

On the other hand, Tiberius uses a 70*148 ram, with a 20mm hardened steel rod, and it seems it's still going strong, even build by me in 2003.