Unless I am misunderstanding the air-over-hydraulic concept you have in mind, the air will still act as a spring in the set up you have described. It would achieve nothing towards what you are asking in the smoother cut. The oil will simply act a medium to transfer the movement back to the air.
If you must push the saw hard into the material (not a good thing) rather than allowing it's own weight to cut, then you would be better off with a full hydraulic system or better yet a lead screw drive and stepper motor. There is little sense in pushing a blade hard into the material being cut. It will do more damage to the blade than it will aid the speed of cutting. Metal can only be removed at the rate the teeth can scrape up a mouthful.
Generally metal-cutting saws are actually limited in the reverse in that they are damped from lowering too fast. They use an hydraulic cylinder and an adjustable bleed valve to control the rate of downward pressure on the blade. Usually around 10 to 20 lbs load on the cutting teeth is about as hard as you can push it and still get good blade-life.