I ran a large router many years ago which used 2 large cylinders attached via chains to the Z slide. The cylinders were horizontal on top of the slide with chains routed around idler pulleys at the front edge, then the chains were attached to the Z slide. Pretty clean set up. The couterbalance pressure was, of course, adjustable which made the very heavy slide effectively weightless. Very cool set up and 'dumb' controls. Could be easily scaled to suit the application.
Hydraulics wouldn't necessarily be too slow, but messy, possibly expensive and overkill. Automotive shocks? - - not enough engineering data or options available to make the right selection for your application.
Adjustable retractors could be used - similar type springs found in a tape measure. These would probably work nicely.
Scott
Consistency is a good thing....unless you're consistently an idiot.