Why not create your own web site and pay for the bandwidth usage that large file downloads require? Renderosity is giving away bandwidth free so that you can show your artwork. In the description put where the full size glorious wonderful 2000x4000 image can be seen, then if someone wants to see it, they can. I dunno where you got the 200k file rule. When I read it it said JPG less than 512kb 100x100-4000x4000 and thumbs 50x50-200x200 15kb. I wont go into texture size versus distance and size of output file, I'll let someone else do that, but play with the JPG compression settings, or don't. Nobody is making you upload your images, however, there do need to be limits.