If you are giving a rest HR, then 55+ is great for most people.
I agree that a rest HR of 78-81 may not need a BB, i.e., while that is a bit high, I don't see it as problematic....how is your HR when you are walking, walking up a gentle grade? If that is below 120 I'd think you're still ok. At your age an aerobic rate as high as 160 should be well tolerated.
These are all "off the shelf" numbers and if your doctor recommends otherwise, then follow his advice.
I don't like taking BB, the side effects are too bad for me at 50 mg as day, but I've taken up to 200 mg per day, and that gives me problems. So, if my resting HR was in the low 80s (70s when in sleeping) without BB, I'd try to live without the BB.
I would take the beta blocker as needed, If the beta blocker was specifically prescribed for your skipping. Of course your Doctor can only recommend this change.
55-60 is Normal at rest/sleep, but not if your up moving around. Mine dips to 55 on its own at rest/sleep. I do not take any meds though. Zach