CLICK ME --> Measuring Bicycle Rims and Hub Flanges

Scroll down for a table showing rim sizes and wheel sizes.
Seems like a I see touring bikes going the opposite way mentioned in the original post - using 650B wheels in 700C touring bikes. This allows more rubber to cushion the ride, space for racks and fenders. The only concern would be reducing pedal clearance to ground. The folks at Rivendell say to draw the BB-drop limit at 70mm (less being better). And you have to make sure the brakes line up with the rim.