DD1:
The 60g is quieter than a regular .22lr, but noisier than the CB Longs that I shoot. The CB Longs are propelled by just the priming mixture, and have the same oomph as the CB caps, which are based on a .22 short case. The CB's aren't much different than the 20g Aguilas that you are using now. I'd be leery of shooting the 60g Aguilas in a populated area. They can shoot thru both sides of a 55 gallon drum and keep on going. While they aren't going that fast, they keep a LOT of retained energy due to their weight.
In populated areas my method of choice for pest removal is a .177 pellet rifle. Depending on how much you want to spend, there are some accurate and VERY quiet ones out there. I have a FWB 124 Deluxe that I got from Beeman's a long time ago. It is deadly accurate, and head shots on tree rats are no problem out to 50 Yds. Paul Watts
Web site went thru it a few years back (re-sealed it and re-sprung it) and it shoots the Crosman Premier 7.9g pellets right around 900 fps mv. It'll group 1" @ 50 Yds if I do my part. I've shot an Allen Zasadny (Phone 319 472-3845) modified for field target use Anschutz 8002 with his moderator (silencer) and all I heard was the hammer hitting the valve and then the pellet hitting the target. Amazing rifle! Spring guns can't be quieted as much as the PCP's due to the spring making a lot of noise.
The FWB will kill a 'coon if you are within 30' and hit 'em in the side of the head. If you get good with a Spring air rifle, any other rifle is a breeze to shoot. Noise wise, once you start moving the pellet faster than 900 fps you get the supersonic crack and it's not too much different than shooting a .22lr.