It's all in the tread.
Well, mostly, if they are otherwise supple tires, being wide shouldn't be a huge performance hit. Compass makes some nice wide tires that won't slow you down much.
If you want narrower tires for some conditions, it might be worth getting a second wheel-set at some point, unless you like changing tires a lot. But they might be too fragile for touring. Conti GP4000 or 5000 might be a good option, as they have very low rolling resistance and tend to run wide relative to their nominal size.