Originally Posted by
TimothyH
If the goal is to get "fitter and faster" as the OP stated then it is best to monitor heart rate. Cadence goes with that.
MPH is a result of, secondary to and dependent upon these.
-Tim-
+1
I say go by HR. And incidentally, getting a HRM is a really good idea for us older riders. Not simply for training, but also for monitoring our health Assuming you have no cardiac issues now, if you ever do, it will be very helpful to have a baseline of what is "normal" for you.
For those who are really serious (not me ), the real answer is training with a power meter.