Personal choice really, also nfluenced by what you're going to use the gun for.
I'm a .22 and below guy so will address that caliber. With the JSB .22/25.4 or even the .22/28.55 you can get a Ghost HP (23" barrel) pushing just shy of 60fpe. In my opinion, 58-60fpe is about 40fpe more than is safe and easily stopped in most suburban backyards in a typical cookie cutter neighborhood. But is enough to play the Extreme Field Target game and/or really stretch out your shooting (100 yards is completely reasonable).
I would suspect the Plus or Carbine (17" barrel) in .22 maxes out around 38-44fpe, but I haven't personally played with that exact combination to know. If a guy was to push a 17" barrel hard, it would be loud and waste a lot of air (reduced shot count). I think the 17" barrel on a .22 Carbine or Plus would be best served as a pellet launcher, using pellets as light as 13.43 and up to 20.83gr on the heavy end. So about 18-34fpe using the typical 870-930fps range that most pellets seems to prefer.
Those are the rough numbers for the maxes from those barrel lengths in .22. The Ghost can always be turned down in fps, but won't get much more than what I just cited above.
The other big thing to consider is length. A Ghost HP with a moderator stuck on the end of it gets pretty long. And if your planning on maxing out the fpe, you'll want a moderator in the end of the shroud.
My personal preference is my custom 18" .20 barrel in a full length HP shroud. All the extra room in the shroud makes it quiet enough to use without a moderator, when pushing 30-34fpe.
The closest commercial thing you're going to get to my custom .20 is a .22 Plus. That gets you a longer than Carbine shroud, and a 17inch barrel. With a modest tune, it should be quiet enough without an additional moderator.
The 17" barrel in Carbine form (shortest shroud) will require additional moderator at even 18-19fpe. The Carbines shroud is so short that it does next to nothing for sound reduction. So a Carbine + moderator ends up being Ghost Plus length anyways. In addition, you get a 480cc bottle with a Plus and only a 300cc bottle with a Carbine.
I'd only recommend the Carbine if max length is high on your priority list. Ie keeping it short is at the top of your list of wants, to the point of being willing to give up shot count for it.