The Smallest Change, The Biggest Improvement

Cleat.

tiniest misalignment on the right shoes mean terrible hot spot to the point that I unclipped my right foot from the pedal and just press on with the left, did that for the last 20 miles during the Dunwich Dynamo.

Taking on more fluids.

I set an alarm on the Garmin to sound every 18 miles. Each time it sounds I should have finished a bottle. Not doing this, in warm weather, at distances greater than 50 miles = rapid drop in performance.

This, the immediate difference from feeling tired to being alert after a small slip of water.