Yes you can use a suppressor with a 1911 by simply getting a threaded barrel. You will need to get a suppressor with a "booster" since the 1911's barrel is not fixed but instead pivots on the link.
I have never heard a .45 ACP suppressor fired, but from what I understand they are not all that quiet. Appearently the larger bore is more difficult to suppress.
AAC is working on a no-holds barred .45 ACP suppressor right now. According to them, they spared no expense in making this the quietest .45 ACP suppressor in existance, by far. As a result it is going to be expensive: in the $1200 range. There are numerous other .45 ACP suppressors out there for far less money: but, as I said, people have told me that they are not all that quiet.
I have a 9mm suppressor that works VERY well. I have it on a Glock 34 but eventually I would like to get a barrel for my other Glocks (17,26) as well as the Browning High Powers. The suppressor is the AAC Evolution 9. According to tests posted on the internet, this is supposed to be the quietest 9mm can out there. When using subsonic ammo it is amazing. I own a couple .22LR suppressors and this 9mm can is almost as quiet if not, AS quiet. It actually sounds almost like a suppressor on TV.
Here is a link for AAC:
http://www.advanced-armament.com/
Here is a suppressor forum where you can read all the stuff I just posted (that is where I got it from):
www.silencertests.com
Obviously there are other suppressor manufacturers out there that produce great stuff. I just happen to like AAC. I have a suppressed Ruger 10/22 and a Ruger Mk.II both by AAC. I have the Evolution 9 and the M4-2000 AR15 suppressor both also by AAC. Obviously I am happy with AAC.