I agree with
@Pagan that the 550fps is outdated, however it was intended to keep players safe with the technology available at the time. Which were AEGs, gas pistols, and bolt action sniper rifle platforms which was either spring or gas powered.
The game has changed with the re-introduction of HPA, but also with advances in the quality of components so now AEGs can handle a higher velocity than they could 15-20 years ago. I try to hold the same standards for both AEGs and HPA and not single out HPA since it's not right.
My personal opinion is that anything that has the "ability" to fire full auto whether it's FCU locked to semi, has the selector plate modified should not have the same FPS limit as a bolt action sniper rifle.
You can modify that gun to fire full auto again, but you can't modify a bolt action sniper rifle to fire full outo unless you're that one guy who put an HPA engine into a bolt action platform (VSR body) which I imagine he's one of the only people on this earth to have done so.
The same goes with an AEG or HPA converted airsoft gun.
Only allow those that have put the money and time in tuning their bolt action sniper rifles to utilize our highest limits. That still doesn't guarantee that they are responsible players, but it limits the user base since you hardly see people using them these days.
I'd favor limiting all other platforms to 500 fps regardless of the technology being used. Regardless if it's modded to semi auto and has a shot delay.