If you read the bike description http://georgenaterry.com/coto-donana-tour/
it says it's designed for loaded touring (she makes another model for lighter touring, but it doesn't weigh any less, according to the specs):
RussSeaton, I'll look into other custom frame makers as you suggested, but I think they are all in this $3500 range , from some cursory investigation I have done. I liked this bike, but think I've convinced myself I prefer 26" wheels for touring.
The Terry bicycle you listed is NOT custom. Its an off the rack bike frame. Terry says it is made by Waterford. Gunnar is Waterford's TIG welded bike name. Gunnar charges $1400 for a custom tour frame plus $400 for fork. $1800 custom Gunnar tour frame/fork. $1500 for a stock frame and fork Gunnar. So your $3500 Terry bike is $1500 Gunnar stock frame/fork and $2000 parts to get to the $3500 total Terry price. The two smallest stock sizes for Gunnar tour bike have 26" wheels. Looking at the specs for the Terry bike, I am not sure you are getting $2000 worth of parts. It would be cheaper, and better, to buy the Gunnar frame/fork and all the parts individually. End up with a better bike in the end. More customized for parts. You could pick a Shimano mountain bike crankset with better gearing than the one Terry provides. Its gearing is too high for touring. 48x11 high gear? Who needs such a high gear? And Terry provides 32 spoke wheels. 36 is better for loaded touring. Your money would be better spent getting the Gunnar stock frame/fork and buying the parts yourself over what Terry is offering. Not sure you need to get a custom bike or not. Just a small bike with 26" wheels should work fine. 26" wheels are correct for your size.
Now, the question of which bike should you buy? If you tour LIGHT, light one man tent, light bag, few clothes, nothing extra, then a regular road bike may be a better choice. If you tour loaded with 4 panniers and lots of stuff, then the loaded touring bike may be best. Loaded touring bikes are not FUN for spirited riding. You can do it. But all the time you are thinking it would be nicer, faster if I had my road racing bike instead of this heavy duty loaded touring bike. So try to figure out what kind of touring you want to do first, then get the bike. Almost all bikes work for almost all riding, but they do have specialization.