There's really no comparison between a suppressed 5.56 shot and a suppressed .45 shot (assuming you're talking subs in the 9mm).
The Osprey is a nice can. Its internal volume causes it to be quieter than most, but the monicore design does result in some FRP. I have no the the 9Osprey and 45Osprey, plus a couple Octanes. The 45Osprey was actually my first pistol can.
The ammo makes a much bigger difference with 9mm. The 115/124 factory loads will be supersonic, while 147/158 will be subsonic. Handloads give you all kinds of options. All common .45 ammo will be subsonic.
We all know that iPhone videos don't do the noise reduction justice, but I keep one handy I made that gives you an idea. It's a 7" 9mm AR w/ and w/o 45Osprey. I loaded a mag rotating through 115/124/147 grain ammo. Two sets without can, the rest with. (I did the same thing with a Glock, but somebody else was shooting at the same time and it didn't come out as good as the AR version, but the performance is very similar).
Enjoy.
http://youtu.be/wNnv4IzBSCk

