I took the advice here, and I brewed my first 10 gallon all grain batch today. I didn't run a stop watch, but I came in about 30-45 minutes longer than my last 5 gallon batch. I attribute that to the fact that it took that much longer for the larger volume of wort to come to a boil.
Another funny thing happened. I got a new weldless kettle to heat sparge water in, and the weldless fittings leaked like a sieve. By the time I got them stopped, by scrounging old gaskets from my cooler HLT, the mash was over and I hadn't even begun to heat my sparge water.
The mash was perfect and the first running were right on target.
So I thought ... oh crap, what now? Then, inspiration. I read about cold water batch sparging on this site, so what the heck, I'll try it! Batch sparged as usual, but with cold water. The way my system is set up I was able to run it through my herms coil and get it up to about 100F on the single pass.
Sparged to my boil volume and checked gravity, expecting the worst. What do you know I was over my numbers! Expected a preboil gravity of 1.039 and I was at 1.044.
The whole batch came in a couple of points high post boil, but the volumes were right on, the plate chiller didn't clog, and I was happy to have two full fermenters.
So, according to beersmith, my screw up cold water sparge yielded me my best efficiency to date.
What on earth? lol