I bought a pocketbook 912 for exactly those reasons (professional papers, A4 format, 2 to 3 columns). We already had two kindles, but I found them hopeless for PDFs.
I am amazingly disappointed. The bugs are really too much. In these days, when you connect phones, cameras and sticks to your PC, there is no excuse for not being able to reliably connect via USB (see
here).
If you feed it a PDF file from a journal which is a bit complicated, the device will take ages to open it, and turn the pages painfully slowly. You can annotate PDFs, with two small caveats.
1. The device is too slow to follow the pen on the screen
2. The annotations are stored in a bizarre html-ish format that you cannot use on any other device.
It has a web reader of sorts, but if you browse JSTOR, I think you have very little chance of downloading a PDF. From other sites, downloads may or may not work.
I tried going back to the kindle for PDFs, but it is as bad as I remember it (I love it for everything, except PDF files).