[Kevin Sevcik]

Matthew, Excel is telling me your file is corrupt, so I can't really look at it.

I'm not an expert at pneumatics, but I'm pretty sure the pressure differential you should be using is difference between your supply pressure and the pressure required to move the cylinder. Yes, at the instant you switch the valve, you have a full 60psi differential, but that assumes 0 psi in your cylinder which means you're not moving. Once you hit the pressure you need to move the cylinder, the cylinder moves (until the pressure drops enough to stop it). So I think a reasonable steady-state case for a long stroke is to assume that your pressure differential is supply pressure minus moving pressure.

That means sizing a cylinder exactly as big as necessary to move your robot is a bad idea, since you'd have zero pressure differential and thus no flow. Which explains why all the speed ratings I'm seeing in SMC's data sheet assume a cylinder sized with a 50% load rate. That is, the cylinder is twice as big as strictly necessary to move the load.