Thanks for all the replies. I changed my profile to reflect the 505.
Regarding the delay, mine might be better than most because I only have about ten books loaded so far. But I do note that one of those books is Our Mutual Friend by Charles Dickens, which I believe is one of the longer books ever written. I haven't really started reading it yet but when I read the first few pages I didn't notice any difference in the page-change times compared to other books I've read on the device.
I wonder if some people just need to reset their device periodically, like a computer...