The biggest illustration I found on DT is that one. I thought what is the point to create such big image and then I realized that when I buy it in maximum size it will gave me more opportunities.
Subject of this image is peoples with big plugs outline black, buying seven illustration would cost me seven credits in small web version but buying this maximum size image I would have seven large illustration (not so large as original but still big) and it will cost only 4 credits. That is some savings.
I took me the same idea with some collage of people. This photo is over 12MP and has been compound from four different photos with the same subject, models and background. So when I buy this photo in maximum resolution for 4 credits it gave me four images in about 3MP, that separately would cost me for maximum size at least 4 credits for each so 16 credits.
That is big savings and big opportunity for all contributors to sell more and to buy more.