Based on all of your requirements I would agree that the 600 would best suit your needs. I think the note pad software and built in calendar will also make for a great assistant for school work.
Also I read a lot of PDFs, books, personal docs and OCR.
Only books are readable without effort. However trying to read PDF on a 6" is not pleasant, even with the Zoom and reflow. You're best of learning how to use tools like soPDF, Briss, Paper Crop, PDFReader. These are tools all found on this site that help reformat PDF to fit on smaller screens.
As far as holding off. Well let me tell you from experience, its real hard to predict the future.
Right now the 600 have dropped in price and 170USD you can pick up a device that debut at 300USD. My feeling is that the new devices might be nicer, but the price might also increase.
My general rule is if I am in the market for a device I do not worry about what will come out tomorrow unless it has already been announced. So far nobody has made any announcements for a new reader.