I have PPQ45 suppressor ready model and a PPQ 5" 9MM with an aftermarket suppressor barrel.
The suppressor I have is a rugged suppressor obsidian 45 and the ammo I was using consisted of Federal 147grain ball 9mm and 230grain Sellier & Bellot ball 45acp.
I've only had the opportunity to shoot them in this configuration once and that was actually last week. The 9mm is definitely quieter then 45acp, while I still need to do some more testing with different ammo, 9mm has the upper hand in lack of noise.
This was my jump into the suppressor world. Mine are still in lock up, but the LGS who did my transfer lets you shoot your suppressor(s) until you get your approval from the ATF to release them.
If you do buy a suppressor I recommend you buy a 45acp can so you can shoot smaller calibers through it.
I also have a 22LR suppressor in lock up that I had the chance to shoot, last week as well. I'll be shooting that one in my backyard when I can take that one home.
Here’s a thought. There are basically 2 issues when dealing with sound suppression; the sound created by the gas when it is ignited and the sound made by the bullet itself breaking the sound barrier. The speed of sound is approximately 1125 ft/sec. or slightly above the normal velocity of a 9mm round fired through a 5” barrel. Therefore you will have to use a reduced velocity round to be effective. If you are thinking of using it as a defense round I would be a little concerned about the degradation of a round’s ability to expand properly.
Today’s 45 round have a velocity under 1000 ft/sec well below the speed of sound while still providing good bullet expansion characteristic. Selection of bullets and bullet types is a lot easier.
For me I would choose the 45 simply because I wouldn’t have to look for a special bullet so the suppressor can be effective. I definitely would not recommend you going out and buying a new gun if you don’t have a 45. All of this deals with defense shooting. If you are just talking about plinking the all time best round is the 22 for and standard velocity bullets are below the speed of sound.
Not trying to be a wise guy, but I think you mean "elevation", not "altitude". When I moved from sea level in Houston to SW Colorado at 7200', it took me about two years of being courteously corrected by natives as to the correct word to use. Altitude is the distance above the ground; and elevation is the distance above sea level.