Here's my second most popular gallery thumbnail.

Bear in mind that most people don't have time to look at every image when they go to the gallery - only the mods have to do that unenviable task. :( One of the main factors they'll take into account in deciding whether to look at your image or skip onto something else will be the thumbnail. Members who are on dial-up will be unwilling to spend ages waiting for an image to load unless they think it will be worth the wait.

With your non-thumbed images, it doesn't matter what size the boobs are, because people can't see them until they've opened the image. By that time, you've got the hit anyway, and if that's all you're interested in, why bother?

If you want to be cynical, do what has been suggested so many times already in these forums. Use a thumbnail of gigantic boobs for everything you post, no matter what is in the image itself. You won't draw the best crowd, and you'll probably get some flames; but hey, you can't have everything. :P