I guess that answers the cadence issue!
I'm 3 years younger and can't get my chubby legs close to 100. A bad knee doesn't help either.
That's the main reason I got into customizing my cassette. With 55 years of smoking, my lung capacity isn't the greatest, but I've found if I keep my cadence within a narrow range of about 5 RPM, I have my best stamina. Being able to shift to a 1T different cog works great when the head wind changes slightly. Also when experimenting with different crank lengths, I could change the gearing for a "best fit".
I ride a "commuterized" 86 RockHopper, so I do have a triple, but I pretty much use it as a 1x8 on the middle (38) ring. I need a good tail wind before I even think about the big ring.
I have to ride very upright because of a bad back, so a head wind kills me!

I guess the question I'd ask is, are you spinning out with the 50-12 combo and "how often"? Going to a 53T ring would raise your top speed from about 32 to 34 MPH.
IF this is for downhill speed, wouldn't it be better to rest, so you have more "in the tank" for the next up hill?