Commenting on spin and cadence. Here are my observations:
In the hour record successes I have witnessed by masters men, the cadence was 100 rpm or greater that corresponds with pro / elites. And of course, him, our Lord Voldemort, Kevin, did 108 rpm at Aguascalientes Mex for his 50-54 his hour record last year.
In 2014, I was training with Dmitry, who was also advising Costa, Froome's training partner. Team Sky wanted Froome to lower his cadence during time trials to the 80 to 90 range.
I have to train to spin faster but I can always elect to spin slower. And it is only in the beginning that cadence affects my aerobic system. As I adapt, my aerobic system returns to normal for the power produced. And I know this because I measure power, cadence and HR.
Also, if I train at the track in the drops at higher cadence, my power riding on the hoods or tops on my road bike climbing is lower (or harder to make) at lower cadence.
I think it is easier to spin shorter cranks fasters.
So experimentation is key with the proviso that we as athletes are highly adaptive and through training and practice can have success across a large range of technology modalities.