Higher temperatures wreak havoc on this Athena. It's that darned surface area to volume problem again. Once this body mass heats up, I'm cooked. The second half of today's run was an 11:33 min/mile pace at an average heart rate of 169 bpm - that part is not so encouraging - it shows that I had to slow down a lot to keep my heart rate down once I started getting warm. Keep those fingers and toes crossed for a cool, calm, dry race day!
My job for this weekend's last major long run is twofold: a) Cover 20-21 miles on foot (8 to 9 of my regular training loops), however I can get it done; and b) get a semi-final check on a race pace by seeing what pace and heart rate I can maintain for that distance.
Right now I'm thinking of maintaining under 165 bpm or ~11:15 min/mile, whichever is slower, for the first half of the marathon, but that still needs some reality-checking on the road in training and with the weather on race day.
I can go a little faster on race day when I'm paced by my training buddy and feeling psyched than a solo training day, so I'll compensate for that by counting only the running pace, and not counting the time that I'm standing still at my minivan hydrating and electrolyting and chowing down.