Everything said here applies. In practice my bikes break down like this:
My road bike (an old TREK) is using 25mm tires and is good for 17-19mph club rides of 25-30 miles on asphalt,
My hybrid is a little heavier, uses 32 mm tires and is good for 15-17mph metric centurys including some gravel if need be,
My touring bike is 30 lbs, uses 50mm Big Bens and is good for 10-15mph doing whatever, whenever, all day, on any surface I've run across.

Marc