Janet-
I am 52, and sort of pear shaped. I'm 5'5" and 140 pounds. The SB medium Tech tights fit me very well- not loose, not too tight, just comfortably snug.
I would say that if you are 20 pounds or more heavier than me but not taller than me, then you might want to order the large to be safe. If you are within 10 pounds of me you could be safe with medium I suspect.
Tell us what your height and weight are, and your body shape- that would help.
I don't have any PI or Cannondale to compare to.