You've kinda shot yourself in the foot because I had a signature that was half the size of that and got told to reduce it. Now you've made a post about it I'd expect the same to happen to you, maybe not. At the end of the day, the reasoning on restricted size is that people don't want to scroll through threads endlessly because people have got bigger sigs than the space their actual posts take up.
A tip. Get yourself a Photobucket account, save the image you like from that paintings site on your desktop or wherever, then upload it to Photobucket and use their editing options to reduce the size. Voila, problem solved for you, and for those who risk wearing out their mouse wheels.
Also, you reduce the size by one third, you can get 3 or 4 of those pics in side by side.