Yes they have been tested and the data has been posted here in this mega thread some time ago.
My valve system in my phantom could not get higher than 265 because the volume behind the valve was not big enough. But I was able to push 50+ shots above 230FPS using a 12 gram and a palmer reg to drop the press to under 300psi. Mathematically my system would allow a 300% increase in flow and eliminates the bottle necking of gas at the PT cup seal. I posted the exact numbers w/ FPS for every shot here somewhere. Splatt got better results w/ his gargoyle.
I also know Yoda has tested his design and had released an earlier design to several people.
Fluted hammers have been mentioned and made with promising results. Valves were made using the madman Rocket valve design to help smooth out the gas flow. I've seen lots of numbers in this thread. All this is proof that the nelson valve system can be seriously improved far beyond just polishing the internals under a buffing wheel.
What design is best? There are fare too many variables.