Value Study

I'm knee-deep in a painting competition at the moment. The task is to pick a master's self portrait and do a caricatured study from it, being as accurate to the original in value, colour, and composition as possible. Naturally, I chose Sargent. It took me about 8 sketches to get to this point, which is the full value study. I did this digitally, but the final painting will be in oils, and in colour. You can the Sargent painting I'm using as my reference here:
[link]