I have one and I bought it new about 8 years ago. As you said it is slim and I also like it's size. I've always preferred the "Commander" sized pistols for the .45 ACP.
I've heard about that problem with the magazine's but I never experienced that issue myself. If I remember correctly you can use P90 magazines as a suitable sub and not have to worry about that problem.
Wolf Springs has factory spec springs for this pistol. At least they did as of a year ago when I ordered a couple of them.
I don't know about shooting the .45 Super in it. I've never tried it. Don't dry fire the pistol unless you have an empty magazine in the weapon because you can damage the firing pin. This is because of the poorly designed magazine disconnect safety. This was a big problem when this model was first introduced. I removed the magazine disconnect and now I can dry fire with or without the mag in the gun.
My P345 has been accurate and very reliable. My only real complaint is the slide mounted saftey. It does not click when using it. You just push it on and off and I've always been a little worried that it would get pushed on to safe when carrying it although this has never happened. I wish I would have bought the de cocker only model.
