Originally Posted by
FreakyFast
However, I would like to take long, on and off road rides, and I think that the bigger tires would be more effecient than 26ers.
My empirical finding was the other way around, although tires obviously vary. I set the course record for the Midnight Century (road & washboarded gravel) for the third time in a row this year on a 26" hardtail. Get good tires and you shouldn't have much to complain about in the rolling-resistance department. RaceKing 2.2 Supersonics are sweet XC-ish tires.
I also took another guy around that route in daylight on his carbon 29er race bike in its Leadville 100 setup (high-end tubeless tires). We tried coasting down the descents together, but I kept coasting away from him. Considering he outweighs me by probably 80-90 pounds, that's all I need to know about which wheel size has the lower rolling resistance.
Rolling resistance is just one factor in performance, so definitely try to get some riding time on each type and see what you like. But if you end up with 26", there's plenty of fast tires out there. In the road-only realm, try some folding Panaracer Paselas with lightweight tubes.
Regarding gearing, I make do with a 44 x 11 on the Midnight Century route and generally finish by heading into Spokane in my 44 x 12 at about 23mph for ~5 miles straight. If you find your bike's stock gearing isn't tall enough, you can always switch up to trekking chainrings, typically 26-36-48.