You're right that they would be faster, in general but the situation in which you'll notice the biggest change is climbing. If you're going for straight speed, I would go as narrow as possible (26 x 1.0") though you certainly couldn't do wrong with a larger tire. I'm currently running 26 x 1.75" Michelin Country Rocks which may be a bit wider than you'd prefer, but they are a nice compromise between speed and comfort.