It seems that the consensus among the biomechanists is still out on whether shorter is clearly better or not.
As for myself, I began riding 150mm cranks on my road bike as an experiment 6 weeks ago and I am now a convert. I can climb, tt & sprint as well as before, with the added benefits of:
-noticeably stiffer crank arms (read 1″ shorter each than my 172.5).
-effectively lower front end from raising my saddle (better aerodynamics and noticeably better high-speed cornering).
-more open hip angle (easier breathing, improved comfort, and better power generation).
-my power stroke now has enough momentum to carry my opposite leg over the TDC dead-spot without needing to recruit my hamstrings to pull that leg up & over (verified on a computrainer last weekend).
I figure most people don’t have the luxury to test different length cranks and end up going with whatever was sold to them on their first bike. I feel fortunate to have been able to experiment and have now made an informed decision. It’s been a fun and enlightning journey!
I’ve enjoyed reading the other riders’ input here on this forum and hope others will continue to chime in with their experiences.