Thanks for the thoughts and opinions.
I was thinking that, at my pace and distance, there is probably a bit more calorie burn when going faster, based mostly on increased wind drag. Although there is the fact that I perspire more when I ride faster.
It's short rides, so I thought I'd increase the speed as I'm capable. I'm not training for anything. It's more about making the rides more interesting.
It's 74 miles a week. That should keep the ticker working pretty good. Jerry Seinfeld said something to the effect of, "Why's everyone getting in shape? What are they getting in shape to do?" Of course, at 57, being able to ride 74 miles a week has to be doing something good for me. Although my neighbors dad is 99 and he never exercised, and doesn't eat any particular "healthy" diet. ???