If anyone has ever shot one powerful enough, is an air rifle breaking the sound barrier very loud? I am just wondering. To me this would negate the advantage you have with an air rifle.
Most of the GAMO .177 break barrel rifles have 1000 FPS capability with standard lead ammo and 1200 FPS with the coated PBA ammo.
I have a Hunter 440 and the crack (sonic = approx 1100 FPS) is substantial with PBA or standard lead with a little lube down the barrel after a cleaning. It will make the neighbors turn their heads even subsonic. I therefore keep my starling and house sparrow shots limited in spring and summer. But in the winter.......
You may be better served with a .22 air rifle for hunting that will not excede 1000 FPS, and less that that to be even more quiet. There are "whisper" rifles now with integrated silencers. Check out the GAMO line.
Never knew there was an air rifle cabable of killing a buffalo. Seen a boar shot with one before but a buffalo, thats crazy.