At high cadence there may or may not be internal friction […]
There’s no maybe about it, at high cadence or otherwise! It may vary a lot from individual to individual, though, if nothing else because some riders have chunky legs with big joints and others are skinny and light-boned.
[…] but there are two major sources of inefficiency;
1) reciprocating losses; the weight of your legs flapping up and down is a lot of energy that is not perfectly conserved
I think this statement hinges on a strict definition of perfectly conserved. If there’s significant energy lost, where does it go? A spinning internal combustion engine does not lose energy to pistons and connecting rods flapping about because they’re balanced by their opposite numbers as legs on a bicycle seem to me to be too. (Of course there are minor frictional loses that go up with the weight of moving parts.)
I don’t see evidence on the road that pedalling nice circles has much to do with performance. You see pretty circles at the beginning of rides and clunky pedalling at the end and that to me suggests, if anything, that pretty circles are inefficient and can only be indulged in when fresh. Besides, those pistons in reciprocating engines don’t push circles and yet the entirety of the work they do is converted into crankshaft rotation.
Froome is a special case in that he uses oval chainrings; this will have an effect on the preferred cadence for any given rate of leg extension in the power stroke.
But their effect is to increase the gear ratio during the power phase of the stroke, so presumably with round chainrings Froome would spin even faster rather than slower.
I'm sure that Sky have shown it works for them, but I can't help but feel that if they were truly wonderful, everyone in the peloton would be using them.
Agreed, and the last Sky guy to win the Tour used round chainrings and a slow, grinding pedalling style even during attacks.
On a long ride at 200W, 60rpm is better.
And yet no-one does this, not even elite male pros for whom 200 W is a comfortable canter. Audax riders at half that power don’t either.