RJMortimer, sorry to pour cold water, but it's probably not the best idea to start from illustrious early holders of the names who "might" be ancestors. I do hope that you've managed to TRACE an uninterrupted pedigree all that way back, rather than jumping to a conclusion that may lead you up the wrong tree. It's not that uncommon a surname, enjoy tracing YOUR Mortimers as far back as possible.
Good luck with your quest though, but please don't develop "tunnel vision" about one starting point way back when. You'll have more fun this way, and be more accurate, I'm sure. I know someone linked to me who has developed an very unlikely "line" back to a really early holder of the surname, and simply will not be budged to look at the real records that others have traced.