I'd go with a QEV on the buffer tank, 1" or thereabouts. That way you won't need a valve with largs ports. Spool valves will limit flow anyway, even if they have large ports. As for the ram, 63mm bore at low pressure for a heavyweight is too small I think. At 10bar that will give you around 300kg of force. I definitely go with a larger ram, 100mm bore minimum and custom built with a large inlet 1/2" or more.