I don't think average speed tells me much, personally, unless I take a split for a specific part of the ride. For me, rolling/flat terrain is a much better judge of speed and effort expended. I'm 44, 6'1" and 200+lbs and try to do a lot of hill work, as improving my climbing is one of the most challenging things for me. Power-to-weight ratio puts me at somewhat of a disadvantage to my lighter brethren, but I can scream on the descents. So I'm fairly crawling up some of these grades and flying down the other side...I try not to pay as much attention to the numbers as how I'm doing for time and how I feel relative to my best and not-so-good rides on the same grades. I don't really have to expend much energy to go really fast downhill. However, on flat and rolling I can push a pretty big gear and average 20-25 for a fair number of miles. Lots of times though, after a day of being indoors/in meetings, I just want to get out and ride - not paying any attention to the numbers, and just enjoying the solitary effort