http://www.overclockers.com/articles373/wbsum.asp
Scroll down for chipset/gpu wbs. Read the entire reviews though; I believe JoeC publishes some higher flow rate data in them if you dig around.
I have a Maze4 GPU in the mail and an MC50 and MC50T already. I was planning on doing a GPU wb comparison at some time in the near future. Where can one purchase the Silverprop GPU block?