Best size for images in a photo blog?

Hi,
I’m finishing setting up my photo blog (http://patrick.dinneen.com) and am wondering what’s the best size for images.

Here’s the same image in two different sizes-
1. 600 pixels width- http://patrick.dinneen.com/all-alone-test/
2. 800 pixels width- http://patrick.dinneen.com/all-alone/

I like the larger as people can see more details in images but on some screens people then have to scroll to view the title and next/previous.

What size do people use, what would you recommend, which do you prefer etc.
Cheers,
Pa.