Hey guys, just back from the Sonystyle store (I just learned a couple of days ago there is one here in Denver). Took a close look at the 300, 600 compared to my 505.
Bottom line is I left the store -- wallet intact.
In comparing the 300 screen with the 505, I see exactly the same thing as I saw with the Astak Pocket Pro. The white of the screen is a slight bit whiter, but so is the black letters and the end result is actually LESS contrast than the 505.
300 was very light and would definitely make a fine reader, but it would be nice if it had more features like the Pocket Pro (SD card, MP3 Player).
The 600 was nice and very responsive but definitely had a reduced contrast and tendency to pick up glare a bit more than the 300 -- but I will say it looked very, very usable.
Bottom line for me is that from where I sit the 505 is still the best of these three and I may look at getting a second one for my backup/additional reader since I've returned the Pocket Pro (due to lots of niggly things).