Those tests measure what they measure very precisely, but do they measure anything relevant to what most cyclists experience?

Are they using super-fit test subjects who can ride the entire test at a given rpm in a given position at a given power output with some minimal deviation ... something most riders simply could not do?

(And is that really what is being measured? How the body metabolizes fuel in two positions? or is the test measuring energy output through the muscles in two different riding positions? Not sure that is "metabolic" efficiency, more like mechanical efficiency ... a body metabolizes food just fine sitting or standing, I'd guess.)

As I understand it, we are talking about a rider who is working really hard just to make one climb, and who is not interested in "metabolic efficiency" or 'mechanical efficiency." We are talking about a rider using different pedaling positions and rhythms in order to extend his endurance, to more fully use all the different muscle groups by resting some (relatively) while working others relatively harder, and switching back.

The absolute efficiency of either position is not important if the rider simply cannot continue to pedal in that position.

When I cannot spin anymore because I might have heart problems, or when a more fit rider cannot spin anymore because of lactic acid buildup in his quads, he might stand up and mash a little to get some different muscle groups involved. He might then try spinning a little while standing to build up a little speed, if he is physically able, and when that hurts too much he might sit and downshift and try spinning again, and on in that general sequence.

The efficiency of energy transfer in one position or the other would matter if he actually had the option of riding the entire climb in one position or the other (as the test subject s might,) but the actual on-the road-rider is switching out of necessity—whether the one position is more or less efficient than the other in the lab is not pertinent because at that moment he only has the option of riding in one position—whichever one he was Not just riding in.

Those lab tests are useful in some cases, but in this specific case, not so much I think.

OP asked and I think the best possible reply, the one most accurate and most useful, is to tell him to mix standing and sitting, mashing and spinning ... and since that is what the pros do, and also what just about every rider here also suggested ... well, he will have to make his own choices.

I know I simply cannot stand and climb all the way up some of the hills (gentle inclines) I face on most of my favorite routes ... and sometimes I have to stand up because I simply cannot sit and spin. The only efficiency I am considering then is how much more efficient it might be to get off and walk compared to trying to ride.