The answer to my question has been answered.
Depending on one's mood, you could summarize this mornings six-mile run as a disaster or just informative.
I call it a Murphy run.
Almost anything that could go wrong - did.
The only thing that did not go wrong was that there were no physical breakdowns.
All tendons, ligaments, muscles, lungs, feet, etc. performed well.
Although I got about five hours of sleep prior to the endeavor, apparently, it was not enough.
My Wheaties ran out at the beginning of Mile Three.
Not sure I can blame the outcome on lack of rest.
Murphy's Law camped for an extended visit.
I could have turned around at that point and gone back to the car and saved myself a few minutes.
But time was not really a factor.
I just wanted to run (as in, RUN) the whole course without having to walk because of some physical weakness on my part.
I had to walk in Mile Three (as mentioned), Mile Four, Mile Five, and Mile Six.
These walks were each about two minutes in duration.
They were because of a lack of strength, which manifested itself in Level Three breathing early in the party and inability to recover to Level Two breathing even on downhill sections.
This was disappointing because as a result of last weeks difficult - though more successful - performance, I purposely cut back on my weight workouts this week.
My leg work was reduced by half, and I cut my workouts from four to three.
Apparently, that still took too much of me to share with my running.
It seems that the amount of strength/effort to run six miles is so close to my maximum overall capability that the slightest deviation from my ideal effort margin prior to a run is fatal to my running capacity.
This makes me seem a bit fragile. (but I AM rather old....)
In addition to my general weakness today, a biological imperative interjected itself midway into Mile three. (more Murphy...)
Fortunately, there was a construction site on the course, from which I borrowed a handy portable plastic booth for a minute or two, to correct the situation.
This problem was successfully eliminated, in spite of adding another unplanned stop.
So, today's jaunt has provided answers to two questions:
1 Can I run the six-mile Cotton Row Race course?
Yes, sort of, sometimes, under ideal circumstances.
2 Can I run the Cotton Row 10k race, in four weeks or so.
Thus, next week I will return to my previous 3.6 mile uphill course.
In one sense, my gambit to run the long course was a success three times.
I did it as planned.
But today proved that I just need to dial back my running a bit.
I would rather run a little than not at all.
And it still is a delightful privilege to be able to run at all at my age.