So thus far I've gleaned from you guys the mash time is extended, the crush is very fine, and the pH must be precise.
Let's keep peeling the onion. How long does it take to drain the tun and what are you guys using in the tun? Braid, tubing with holes, false bottom, etc?
I use a fine crush with malt conditioning to make sure the runnings drain fast. I balance my water to hit a mash of ~pH 5.4 ± 0.1. I typically mash about 75-90 minutes. I do like to do an alpha amylase rest around 158°F, which does seem to speed conversion. I use a braid with a dip tube to the bottom of the tun, which allows me to drain all but the last cup of water, leaving almost no dead space.
I stir at the end of the mash, vorlauf about 1 quart, then drain as fast as it will run, taking maybe 5 minutes to fully empty the tun. When optimizing my system, crush seemed to be the biggest variable. If you are interested in getting complete conversion, I suggest that you read Kai Troester's site, learn how to start measuring conversion efficiency and figure out what gets you over 90% on your system.
Lately, I've been using single infusion mash for 90 min on my Brutus 10 system. I use a Blichmann 15 gallon kettle with a false bottom...works flawlessly.
I like to recirculate the mash with my March pump until the wort clears (usually 15 min.) then pump into the BK which takes about 5-10 min to pump 7 gallons of first runnings. I typically get about 1.075 with 25lbs of grain at a 1.5:1 water to grain ratio.
My estimate is that would be about 66% mash efficiency, depending on how much you boil away to get to 1.075.