There are various kinds of proportional and servo valves alec, the latter sometimes use pwm, but the former, all the ones I've come across do use pwm.
For a cylinder over 3" or so a dual stage valve would be required, this is usually accomplished via a smaller proportional valve, or i to p as they are referred to as, followed by a pilot controlled pressure regulating valve, the pilot pressure comming from the i to p, this then followed by a directional control valve to obviously control direction, parker do these all in one, and they cost £££'s.