aerodynamics after adding bags

You need to look at how people manage long audax rides. They're doing what you want to by touring at a good average speed for days. They usually use road bikes or dedicated light touring bikes.

The main point of my first post is that if you rely on putting the bulk of luggage on a saddlebag like the Alpkit Koala then the bike becomes really top heavy and a pain at low speeds, especially if you need to man-handle the bike as it will want to fall over. If the straps work loose at all the bag acts as a big pendulum.

Lightweight touring and alternatives to heavy-duty camping & touring gear is a hot topic at the moment. There are lots of people pushing alternative luggage. Alpkit have been developing all sorts of bags and I have noticed Condor have their own luggage range now: http://www.condorcycles.com/Luggage/View-all-products.html

I've bought a touring bike as I have accepted that I do want to take weight, go camping and rattle down some by-ways. It's essentially replaced my mountain bike. I would like to build up an in-between bike at some point too, as much as I love the touring bike it is slower!

Having used my CAAD8 with a large saddle bag from Alpkit and other stuff in drybags attached to the frame I gave up and bought a touring bike. Racey geometry with weight high up will make your bike horrible to ride and difficult to maneuver in traffic. There definitely is middle ground but I suspect it involves using a rack and placing the weight as low as possible in a slim profile and a handlebar bag. A frame bag looks like a good idea but I imagine is a pain in a side-wind.

Don't underestimate the amount of food you'll need either.

Yup, your'e either Wiggo or Mr. Bean. i couldn't find a middle ground...

Comfort should be your 1st consideration, more comfort will equal less fatigue, less fatigue means a more consistent pace, think of the tortoise and the hare.

Give up all hope of remaining aero, but this should not be your big concern. Weight is the big issue, you will significantly raise your center of gravity and you will come much closer to the weight limits of both the bike frame and the wheel limits. You also want to consider 28's if your frame will allow that width. Did Bordeaux to Santiago de Campostella on a CAAD8 with Conti 4 Seasons (the same ones we did Paris-Roubaix and the Tour of Flanders Psyclo) and ended up with an average of 2 flats per day, all pinch flats and got slaughtered on every hill. Average speed dropped from low 30's to mid 20's, so a 10% increase in weight yielded a 30% drop in speed. PM me if you want to go into details.

If you are putting that much baggage on a bike, then I kind of thinking the aero profile of the frame is not too much of a concern.... I would be looking at a bike more tailored to long distance comfort.

...and if you've not even bought a bike yet, I suspect your idea of 'fast' and the reality might represent something of a big gap...

If you want to ride an aero bike and go super quick, get a car to follow you with your clobber in the boot.

Aero bikes are aero in the wind tunnel. When you put a big round lump of meat on the top they are not very aero at all. When you put meat and bags on top they are even less aero.

Look at the bikes used for the round the world race for ideas:

It's difficult to say for sure, but I strongly suspect that having an aero road bike will make no improvement you your speed, and might make it worse.

Firstly, the aerodynamic design is based on having an unimpeded flow of air over the frame. This isn't the case here.

Secondly, drag is dependent on the square (arguably cube) of velocity. So the faster you go, the more benefit you get from an aero bike. So on a 10 mile TT, great, but on a long tour you won't be doing those sort of speeds and any benefit will be negligible.

In short, you are better off on a bike on which you can be comfortable and relaxed - this will gain you more time than any aero gain.