well, guys and girls, let me just add this datum:
when the medicos were watching my heart, they got really uncomfortable when I'd drift below mid 40s at rest. My oxygen level was fine, just slow heart rate. They'd mumble about brachycardia and slap me around a little to get it back to a higher level.
subsequently had the ablation procedure for atrial fibs, and my resting pulse is now waaay higher... 70-80.
on known hill climbs, tho, there seems to be no difference between when I did it with a resting pulse below 50, and doing the same climb now with a resting pulse of over 70. In my case, resting pulse doesn't seem to indicate much on the bike, and, remember, always, keep it above 0!