first off, sorry nun to use your thread for nick h.
nick - up front, let me admit that i don't have the technical data on carbon strength, fatigue resistance, etc. neither do i have anymore experience riding one other than taking a friend's out for a spin, so you're personal experience quite possibly outweighs what i'm about to say. in no particular order:
one thing is that you mention stuffing that rear bag full and strapping camping gear on the outside. even ultralight, it sounds like a lot of weight, unless you you mean a 1 lb. bag, 6 oz. pad and an 8oz. siltarp. if you're planning to usually find accomodations and only fall back on these on occasion, all well and fine. but if you're planning on such a set up daily, i know from personal long distance hiking, that it becomes psychologically challenging after a week or so. (well, the up-side is that, because of the constant exposure, you find yourself getting up and moving as early as possible and putting off stopping for the night as long as possible also, which makes for covering a lot of ground.) if you're planning on using a tent and maybe cooking gear, etc., i really wonder if that bag will hold up. a traditional rear rack would inspire more confidence, but i don't see that you have any braze-ons for mounting.
so... if you're going to be carrying any appreciable weight on the rear, the small number of spokes on your rims would also appear to be a weak spot, in spite of the structurally strong cross-section design. what things can handle from time to time with only the rider's weight can be quite different from what they can handle on a daily basis for months, and with "x" number of pounds centered over the rear and can't "post" when it sees a pot hole coming up.
my longest tour ever was about 2 months, of which about 3 weeks or so were spent riding in mexico. all kinds of things can (will?) happen. it's quite different from a week-end jaunt. washed out sections of roads, deep gravel instead of paved shoulders , big trucks on small roads forcing you onto non-existent shoulders, to mention only a few from personal experience. a bent derailleur hanger, having some of your strapped on camping gear get caught up in your spokes or something of that magnitude is not unlikely in a trip of the length you're planning. how would something like that affect your attempt?
i guess what i'm saying is that i personally wouldn't decide for the milage gained by a titanium/carbon bike over the many more miles lost when something goes wrong.
while i may not be that much of a gambler though, i can understand that in making record attempts, a gamble that pays off may be the only way to go.
best of luck!