I brewed today and came in 8% lower efficiency than usual average. I guess I will know for next time I use the 10 gallon.
Also it was harder to keep the temps up during the mash. I usually lose about 2ºF in an hour in my 5 gallon, but I lost 4ºF in the hour using the 10 gallon mash tun. I guess the larger thermal mass of the big cooler has a higher coefficient for heat loss. For 5 gallon batches anyways, doing a mash that uses more of the cooler space probably will have better results.
I have read that most of the conversion is done after 15 to 20 minutes anyways, so I wonder about how important maintaining that temperature is. Any of you guys that use recirculating systems notice any differences with that ability to hold a steady mash temperature for the hour?