As far as carrying stuff is concerned, think about a Carradice Nelson longflap that fits to the loops on the back of a Brooks B17 saddle (that is, if you choose a B17, but the Carradice can be adapted to other saddles).
The longflap can stow a helluva lot of gear, plus stuff on the outside if needed, and doesn't need a rack at the back (which may be an issue if you choose a bike on your current shortlist that doesn't have rear braze-ons).
Matched with a decent-sized handlebar bag and the additional support frame for the bag, the Carradice might enable you to avoid the need for a backpack, unless you want rehydration. And you could probably do a Carradice/bag frame/Brooks deal with Wallingford Cycles.
You need to look at the geometry of a bike as well as its componentry. For what you want, the suggestion for a randonnee-style of bike is a good one -- a good lightweight steel (look for Reynolds or Columbus) frame and fork, with reasonable-length chainstays (430 to 450mm) for a comfortable ride, would seem more important than going the expense of installling a CF fork (I like CF as a frame material, by the way, so I am not dismissing it as an option, but the weight-saving probably wouldn't be significant versus price).
I wouldn't consider anything less than a 25C tyre -- I am around 85kg (187lb) and I do a lot of riding on 25C tyres, and find them good for speed and, at moderate pressures of between 80 and 100psi, comfortable.
Speaking of tyres, the other strong items you will need are wheels. They are often overlooked until they let you down. I have Velocity Aeros on one bike, and these mid-weight rims have proved to be durable. At your weight, a good build with Ultegra hubs and 32H Mavic Open Pros might be a good, durable option -- certainly the roadie guys like that spec for their almost unchallenged durability for their weight. I would suggest avoiding anything less than 32H wheels, and 36H might be even better to have.
You will likely presented with a few options in gear shifting. Shimano STIs are proving to be very reliable these days. I wouldn't consider Dura-Ace because of its expense. I like Ultegra, and I have had excellent service out of old Tiagras. 105 also seems to get a positive from many.
You might have bar-end shifters as an option. I'm not into them myself (yet) and I likely won't ever spec them on drop bars.
For the journey you are considering, comfort that evolves from good bike fit will be paramount. It shouldn't be just "vaguely comfortable". There is no point in having speed if you are crippled with pain at contact and other points of your body at the end of each day.
Unfortunately, choosing a suitable bike is that much more difficult if you aren't able to test ride them any longer than around the car park. I don't think I saw mentioned in your post the type of bike you ride right now, as a comparison or starting point.
One thing you will need to do after acquiring your choice of bike is to get to know it intimately from a riding perspective (from a mechanical perspective, too, if you are so incined). That means probably doing a few extended weekend trips away with the gear you intend to carry the way you intend to carry it. You will fairly quickly find out (a) if there are fit issues with your bike so you can fix them and (b) functional issues with your gear.
Good luck, and don't forget to look up at the scenery from time to time... it's easy to get the head down in the name of speed and not appreciate what's around you.