I don't have the bodies you are interested in but do own the 18-200mm lens. Fine lens, but it does have distortion at the 18mm range so I'd be pairing it with the new 10-18mm if I didn't already have a better lens in the 18mm range. I'd consider bringing the Canon 50mm f/1.8 for nicer portraits and it doesn't add much weight (or even the pancake 40mm).
I guess it's all a matter of opinion, but as much as I wanted to like that lens when I was shooting crop, I was pretty disappointed. Slow focus, lens creep, not as sharp as I had hoped... Since I've moved up to the 6D, I haven't touched my old crop rig or the 18-200. Actually meaning to sell it for whatever the market will bear.
My last trip was with a 6D 24-105 kit, and my 40mm for when I didn't want to carry around the zoom. The pancake is sharp and makes the setup quite small, and the focal length was great walking around Austin.