you know, the more I think about it, I think that on my bikes with 175 cranks, I probably tend to spin a bit slower compared to my faster bike that has 172.5 on it. I realize my touring bike 175 is generally used with 40+lbs of stuff on it, and the faster bike 172.5 is used with hardly anything on it, and often riding hard and fast---but I do suspect that the longer cranks help with pushing a heavy bike along, as each pedal stroke generally takes more effort throughout the stroke.

again, I dont know if this is all in our heads, and I'd love to be able to do a back to back switcheroo on the same bike, same day, to really be able to see if we could feel a difference.
I still suspect that we adjust our "natural feeling" cadence for whatever setup to a certain extent, and I also suspect that unless someone is really short, or really tall, the differences are pretty small.