You can see the differences between the 350, 650 and 950
here at Sony, including size and weight for each.
I'd also suggest the 350 as well that meets all your requirements. Not sure why you ruled it out, it's also touch screen identical to the 650 and 950, just has a 5" screen which makes it extremely easy to take with you everywhere. It's also true the text is slightly darker because it's the same resolution as the 6" screen as others have pointed out. The main difference between the 350 and 650 is that the 650 has an expansion slot, the 350 does not. But do you really need to keep more than 1000 books with you at any time? The smaller size of the 350 is perfect, I end up taking mine everywhere with me and it easily fits in any pocket. Not sure I'd trust it in my purse because of how I cram stuff in mine even on the rare occasions I do carry one, unless you have a flat side pocket where it won't get pushed on by a wallet or keys and possibly crack the screen.
Any of the 3 Sony models though will be easy to read in daylight as they all use the newest e-ink pearl screen, not color. If you're using it primarily for reading, I wouldn't recommend bothering to even look at color devices, they will be harder to read outside in daylight.
I just got my 350 on sale for $129, and I just noticed at the Sony site that they're offering $50 off on the 650 also. That sale might end today though. If you can pick it up somewhere local today that has a full return policy if you don't like it, possibly Best Buy, I'd strongly suggest that so you don't miss out on the $50 savings.
Calibre is terrific to use as your sole manager for your ebooks and ereader and will make transferring books over to the reader very easy, and conversions so the Sony can read them as well. There's a very active subforum for Calibre here where you can get any help you might need with it.