Taking JB's heat acclimation advice into account, we didn't go crazy today - just rode out to the start of the loop and back (probably about 38 miles - it's close to 20 each way - I had a small gap where I didn't turn my Garmin back on right away after a stop, but numbers are close enough).
Very negative thoughts in the first half of the ride - I ignorantly declined Brent's offer to lead the way, which meant I was scrambling to try and keep/catch up and feeling horribly and negatively slow. We stopped shortly after the halfway point for water and nutrition, and I had the sense to suggest that really I had better lead the way back - once I was in front and setting the (slower!) pace, it was infinitely better. The ride home felt like it took about a quarter as long as the ride out - some of that is wind, much of it is purely mental plus blood sugar!
Now I think I know the turn-offs (really it is a virtually idiot-proof route, only of course there always are one or two places where someone like me can potentially go astray), and can do it by myself next week. That is good! The point of doing it at 6am on Sunday morning is that there is truly very little traffic - it is not a stressful ride, though I can see that the ride home later on a Sunday morning will be more trafficky and potentially problematic once my rides get significantly longer. But sufficient unto the day...
Anyway, 36.78 miles, 2:21:55, 15.5mph avg pace, avg HR 133, max HR 154