I tour with a Surly LHT which sports 26" wheels. I'm fine with them when solo. However, when I ride with my two 700mm equipped tour mates, I have to work to keep up with them. On our 700 equipped road bikes I am the faster rider of the group.

My point is, it is my opinion that 26" wheels are noticeably slower than 700 wheels. On climbs they also lose downhill speed (momentum) much quicker than 700s. In our tour group's case my 26" wheels are the great equalizers.