I got up at 4:30am, was on the bike by 5:15am. By 9:30am I'd done 60km and 1500m of ascent. I felt totally fresh. Sure, there were some climbs I pushed - single speeding is like that round here - but whenever I jumped back on the bike I was straight on the power with no problems or effects from any calf tightness.
At 80km (half way) I still felt good, though it was getting hot now at 11am. At 100km I was at the top of the Gap which turned out to be a bit of a struggle. The next 20km were a bit rough I think due to lack of fluid and insufficient food. I picked up a bottle of pop and wedge of bara brith at a cafe and this kept me going to the end, to the extent that I pulled off a KOM with 140km in my legs (having tried unsuccessfully to get it before on shorter rides).
Now 4 hours after the ride, I've eaten most of the food in the house but my legs feel great

Thinking about why moving your cleats back work relates to which muscles do what when you pedal. The ankle is an inherently unstable joint. It needs tendons and your calf muscle to prevent it folding up under your weight. The knee on the other hand is an inherently stable joint that doesn't use muscles to keep it straight in a standing position. This is why your calves ache and not your quads/ham strings when you've been standing for a long time.
So, with the cleat under your ball of your foot - the traditional position - the calf has to work quite hard to counter the effects of you pushing down with your quad. The harder you push, the more your ankle will want to deflect and the tighter the calf needs to be to prevent it. The two muscles work against each other. Moving the cleat back - in my case by15mm - means that the length of the lever (i.e. Your foot, as measured by the distance between the cleat and ankle) is shorter so the calves don't have to work quite so hard to support the ankle when you apply force with the quad. That means for the same force applied by your quad you go faster and because it is more efficient and because you're using the calf muscle less causes lass fatigue. The latter is evidenced by the fact you can get straight off a hike-a-bike section and onto the bike and pedal off even if your calves are screaming at you (I did just this several times today). The former is evidenced by the string of KOM's and PR's I've picked up over the last three weeks.
If you haven't looked hard at your cleat position yet, what are you waiting for? Seriously. It will transform your ride. There's no way I'll be going back to the traditional position now, that's for sure.
Here's a link to the ride, which some of those on here have seen already - thanks for the kudos!
http://www.strava.com/activities/168526869