I was not entirely sad about moving away from pneumatic pistons. Such a setup would make my build too similar to a steampunk design, just imagine the sound of it while running. I'd prefer to lower the noise level if possible. I had several full metal gear servos in my toolbox:

For instance the MG995 (that I had available) specs show:

Operating Speed: 0.13sec / 60 degrees (6.0V no load)
Stall Torque : 15 kg-cm (208.3 oz-in) at 6V

Definitely promising, considering my idea was to use 6 in parallel.

However the tests came out bad: the entire setup had very little power, making it unusable for the project's purpose. Probably better servos could still have this, but I don't have other models to try.

Time to try something else.