So I think the problem has been solved but it might get me playing around to try and find a faster skin for my particular setup.
Other than the option to include a zip file of the original images, which isn't present in most skins, the choice of skin isn't going to make any real difference. Just leave that zip file option turned off.
The thumbnails and slide images will be the same size, regardless of skin (assuming the same image bounds), so the upload size won't be any different. The time won't change.
The only real solution is to move.