What sort of books do you read? If they are mostly text then the big screen might not be necessary as you can use a program to cut the PDF pages up so they fit nicely on devices with smaller screens, and still have large, readable text. If the formatting isn't too complicated, the Sony can reflow the text in which case no conversion is necessary. Otherwise Calibre is quite good at converting PDFs to other formats.
If you are reading textbooks which have lots of images, I think you do need a device with a larger screen. I was impatient to get a new digital reader so I snapped up the DR1000S and am very pleased with it. There
may be other large devices coming out this year with more features and a better price.
Netronix,
Jinke and
Onyx have said they will release 9.7" devices but I don't think there are any firm release dates. The Plastic Logic device
looks very nice but it wont be out until 2010 at the earliest and we don't know how it will handle. So there is a good chance the DR1000 will be the only large e-ink device on the market for a while.
Are you determined to have e-ink? If not, a subnotebook or a tablet PC might be worth looking at. I had a tablet and found it too heavy and the battery life too short to be useful as an ebook reader so I would recommend e-ink.
By the way, since those iRex DR1000S reviews were written the battery life has been significantly improved and many useful features have been added. There are still a few annoying bugs but it is definitely a much better device than it was.