After reading up on how loud some of the 45acp silencers are I doubt I will head that route. The 9mm subsonic can get very quiet and I want something that is nice to use with no hearing protection.
Over in the nfa forum of this site someone has lots of measurements for how loud a silencer happens to be. There are links to a site with the measurements.
In one discussion someone said that running a 308 bullet through one companies 308 silencer was X. It then was mentioned that running a 308 bullet through that companies 338 lapua silencer was also just about X. The lapua silencer was 2 inches longer and maybe a bit bigger around, I forget. Anyway, there is more to what makes a silencer work than how well the bullet fits the hole in the silencer.
For best results you should of course consider going with a silencer for each round, but that gets expensive.
And if you have a handgun that takes aftermarket barrels, like a glock 40s&w and you want to use the 9mm aftermarket barrel in that gun, you have some versatility.
The biggest thing to keep in mind is that you have to be able to fit the silencer to the gun and there was some discussion about that being a problem if you want to use one silencer on several guns. If you are using aftermarket barrels in the gun then the outer diameter is the same. If using several different types of handguns the outer diameter may not be the same.
The only problem with reading up on silencers is that I am not interested in one of the 44mag bolt guns a couple make. They are quiet and very accurate. I think it would be great to not bother the neighbors while shooting.