Humidty - as far as FPS at the muzzle it isn't much of a concern to me, until i start getting out about 100 yards - then the 'thicker' air starts to actually start showing up POI differences. the specialty type as mentioned above has it's drawbacks when launched at longer distances, but within 75 yards and depending on if your rifle likes them, work pretty good when trying to be discrete. of course the slower stuff will drop more than HV, but generally be more consistant / accurate at any distance.

Over the travel of the bullet, you'll have more stability from muzzle to target as there's no transonic stuff going on over any of the trip there. the trueist of labeling is the aguila with super subsonic designation, which in my opinion is like a generic term that describes CCI quiet, rem cbee, CCI cb both in FPS and sound, getting below 700 fps 10 ft from the muzzle. The truely really slow / quiet stuff should have a specialty type branding on it including the CCI quiet, rem cbee, CCI cb, and the like that have a majorly reduced powder charge, or even no powder at all and relies on the priming agent to propel the bullet. The closest thing i've found that matches up with the print on the box is. IMO a fine example of subsonic gimmic on the box is remington subsonics, through a chrony i've recorded the same FPS 10 feet from muzzle as wolf extra & match, yadda yadda. so anything under that 1080 / 1120ish print on the box is really subsonic as it never goes past the speed of sound (depending on extreme environmentals). Technically, match / standard velocity type ammo is subsonic as it's below the speed of sound from muzzle to target.

.22lr subsonic ammo