Just looked at the Joan of Arc tutorial - seems to make the job much easier than sticking to the 'edge extrude' method.
For the record (and not for the thread hijack), here's my latest effort. Took me about four hours in total:

My main problem areas are the nose and chin. Also note that the ears are deliberately in shadow, because he doesn't have any.
For the record (and not for the thread hijack), here's my latest effort. Took me about four hours in total:

My main problem areas are the nose and chin. Also note that the ears are deliberately in shadow, because he doesn't have any.