CCI CB Long and Short have the same amount of powder and same bullet, just different cartridges. In my Rem 597, the batch I bought chrony at between 500-600 fps (pretty wide spread for sure). That is way below supersonic. Only useful within 50 yds max, as acceptable accuracy drops off quickly after 25 yds.
As for quiet, I shot a couple in the basement one evening to test their penetration in 1" oak and no-one upstairs noticed. There is simply no quieter 22 rimfire ammo available, and they are readily available.
BTW - they embedded themselves completely in the oak at 10' - plenty of energy for rabbits at 25 yds. Of course you would only shoot where legal, but sometimes you don't want to advertize that you're shooting, or simply don't want to bother neighbours.