After years of riding different types and styles of bikes, the variance of crankarm lengths is notable when pushed hard. For me, I like to ride everything but regarding crank length and determine what's appropriate, I use a 'feel' by how much the knee pains. I leave the math for the rest of it.... wheels, chainring, gearing, etc.. If the knee's really feel it, I'll change out for a shorter crank arm. Might seem odd but usually works for me. Also, as we age our joints naturally degrade and progressing to using shorter crank arms does help.