PH, I think the type and weight of the bike is very significant for doing 'fast' long distance Audax rides.
My main Audax road bike is a Seven Axiom Ti, Campag Record, 23-622 tyres etc. It weighs about 17lb (7.7kg) with mudguards! I always ride audaxes with the bare minimum of luggage even for over-nighters. I can manage 200's within 8 hours, 400's in 20hrs, 600's in 32hrs. On my local training rides (pretty flat) I consistently average 28-30 km/h.
OTOH, my Raven Nomad, flat bars, no racks, 50-559 tyres weighs 33lb (15kg). On the same training rides, I can barely manage 22-23km/h, for what feels like more effort! Clearly, my audax times would be a lot slower on the Nomad. (I don't think I'd want to ride a 300+ on a Nomad, though)!
I realise the Raven Tour isn't quite so heavy and cumbersome, but I hope you get my drift. (Your 14 mph average is the same as my Nomad average...).
BTW, my racing audax bike is as comfortable as my Nomad.
Shaun