I did some more exact calculations on how much surface area is available for air flow through poppet valves vs the sliding valve. The slider has a slight "fully-open" area advantage. I based the poppet valve numbers on the biggest diameter valves that will fit in the FS40 cylinder, with a lift of 2.6mm (which I measured from the Alpha 56). Taking into account the very quick opening and closing mechanism I've got planned, area under the curve should heavily favor the sliding valve.

I can't wait to be able to work with more than numbers and drawings.