I tried mounting a Carradice Nelson Longflap bag to my Cervelo RS, an endurance/plush/relaxed-geometry road bike. Absolutely
hated the way the additional weight made the bike handle! I bought a $100 Nashbar aluminum touring frame, bolted on some parts-bin components, and built some wheels. The geometry of the Nashbar touring frame was
phenomenally better than the Cervelo RS when I mounted the Carradice bag. Plus, the Nashbar was so cheap I didn't have to worry (much) if it got stolen...
If you
do go the road bike route, you'll need a way to carry your gear. For "credit card" touring, you might be able to get away with one of the various Carradice saddlebags, possibly with a Bagman support (if your saddle doesn't have the loops for hanging a bag). If you want to carry more stuff, you'll need a trailer or racks plus panniers. Since a road bike won't have the braze-ons necessary to mount racks, your options there will be somewhat limited.
Tubus and
Old Man Mountain have both front and rear racks that can be mounted to bikes that don't have braze-ons. Wayne at
The Touring Store carries Tubus and is supposed to be very helpful. Trailers are somewhat easier to attach that racks and affect the bike's handling less. The disadvantage of a trailer is that you have more tires to maintain, it's heavier than a set of racks, and it makes the bike much longer.