I think he was commenting on this: "there's no reason why the FPS limit shouldn't be 400".
The question here is also depending on the facility. CamoGames has stated that there are hallways as long as 160 ft. in his facility. Even a 400 fps shot will have lost quite a bit of energy by the time it reaches a target ~100 ft away.
I would say that 400 is probably OK as a maximum, but to err on the side of caution would be better for this 'trial run' and go with 350. Remember, it's not like everybody's guns are tuned to be just under these numbers, some people have guns that shoot less than 300 and keep them that way so as to not affect an already excellent performance.
To those who would not play if we had an imposed maximum of 350 fps: Have you played at these velocities before? Even if you have and had a bad experience, please consider giving it a shot
for the sake of having one massive, awesome, time of your life type of cqb game. And yes, pun very much so intended....
I think 350, full auto, full face protection optional and eye wear mandatory are some sound rules.