I've been using Adobe PhotoDeluxe for years but didn't realize they could "Prepare a photo for online display". With the new, improved PetTalk, Avatars, etc. in mind, I went to PhotoDeluxe help and searched for "Online display". That's where all my questions were answered; reducing file size, resizing, pixels, resolution, etc. Hopefully this information will help you find the answers in your software.

My pet peeve is having to scroll across to read text and see entire pictures, so I've been using 400 as maximum pixel width. I might experiment with 500, but 640 is too much.

I started posting pics just this month, I'm definately not a pro, but my experience might help others.

I couldn't get Webshots to work correctly, so I switched to Photogra. Not a big deal since I only had two pics to switch.

Good luck