You can see how I decided half way this new piece to try a new technique - namely gridding and using my PC for the reference picture. I hated erasing, and sometimes sanding away the mistakes, only to erase them again because something still wasn't right. So the gridding makes it alot easier, and because I'm confident in the proportions now, I can work alot faster (which is still slow since Portrait is a new genre for me) and focus on other areas. We'll see how it turns out!
(Being my first portrait commission, I am glad I took the plunge and tried this new technique! - thanks CataclsymX for the proportions tutorial!)