Again; one cannot merely look at a cyclist's pedaling style and determine the cyclist's force production throughout the stroke, so yours may look round but actually be less than you think in terms of force production throughout your stroke. In addition, multiple studies show there is no significant difference in muscle activation between seated riding on a flat or grade (there is significant difference in muscle activation standing on a climb), so I am not sure of your story's point regarding "feeling." Personally, I always feel sore after looking climbs 1) because I am riding hard 2) because there is no time for recovery.
Here is the Dr. Coggan's take on pedaling is circles:
"...It would also be interesting to see the data upon which he bases his
conclusion, since it runs counter to the only published data that I am
aware of that has examined the relationship between pedal force patterns
and efficiency, performance, etc.
Somewhat ironically, when I was doing my Ph.D. w/ Ed (Coyle), he too had the working hypothesis that somehow "spreading the work around" to different muscle groups made a significant difference...but first we found no difference in metabolism or performance between pedaling w/ or w/o toe-clips, or cycling vs. running uphill (in high LT cyclists), and then subsequently he found that the best performers were those who simply stomped down hardest on the pedal, i.e., NOT those who "pedaled round". Despite these data, though, the idea still seems to keep coming 'round again (pun intended)..."
Indeed, "pedaling in circles" is myth without substantiation that won't die, kinda like tubulars having lower rolling resistance than clinchers.
PS did you save your power meter data from the above ride? Since it sounds like a great person best and something to have objective data to analyze.
Finally, the reasons why speed records changed starting in the early 80s (actually 90s) are primarily twofold 1) Much, much better aerodynamics 2) hematocrit manipulation. You can take 2) to mean whatever you want (hypoxic training?), but when hour record data is analyzed in terms of watts/kg, there is a power spike starting in the early 90s that cannot be explained by improvements is mechanics or training.