I'm on dial up so they are painfull!!!...that means often they don't even down load, and I wast a lot of time waiting for down loads I don't necessary want to see.
Problem I have, I can't afford broadband, and with family, job and other committments I do not have that sort of time it takes to down load and refresh pages.
I thought the size was fine, may be a little bigger, but not the size you have them. Otherwise it may be that you reduce the number of posts per page, so people don't have to down load a lot of stuff they have already seen (as a regular)
A minor point but having larger thumbnails makes it harder for a poster to judge whether a submission was of interest of not. What does it tell you if 100 people view the subject page and 2 click on the thumbnail.
Was the attached image simply of no interest or value? Or was it appreciated by viewers who got what they wanted from the large thumbnail and so saw no need to click? How would the poster know?