Hence, you have your dilemma Schecterman, as the file size limits here at Renderosity are at a hard 150MB for downloads, and most places I've seen have similar limitations, you would be hard pressed to find anyone who uses those formats (to my knowledge). Content Paradise has the highest limits that I've found at 750MB for file sizes. As to your last point, the memory and GPU usage will defer based on the complexity of the image (eg. if there is transparencies). Another reason for this is that having one picture as a jpg and the same picture as a png will normally result in a large difference in file size. Especially with texture files which require many details, you wouldn't possibly be able to have the same file size for the same image across the formats (again to my knowledge). If I'm wrong do please let me know as you have now piqued my interest in this. Going through school for game design, we were all taught to use the lowest possible denominator as memory usage/allocation/budgeting is critical in games. I'm still learning as far as actual 3D goes outside of games (typically low poly, low to high resolution textures) and am always happy to learn more.

I will try to look out for something for you, but good luck either way in your search.