I just completed my first BIAB using EdWorts Bee Cave porter recipe. I mashed just under 14lbs in 8.5 gallons of water in my 10 gallon pot - it was full!. I ended up with 7.5 gallons of wort after squeezing the piss out of the bag, BeerSmith says I hit 76% efficiency pre boil. I did pull the bag after an hour, raised the wort temp and then put the bag in for a 10 minute mashout @170. I used a round grill grate above the kettle to hold the bag while draining, and did I mention I squeezed?
I also learned a few lessons, first don't underestimate the weight of the bag, it's heavy, somewhat awkward and I really should have had another set of hands if only to slide the grate below the bag. Also hitting mash temp is tough,, different calculators gave me different starting temps. Before filling the bag I panicked about having enough space and pulled .5 gallons out. I ended up being low on temp and used that water (after heating in microwave) to help hit my mash temp. Next time I will probably hold back a gallon and have one gallong of boiling water and one of cold ready to adjust temp. I also learned that 14lbs is the absolute limit with my rig, I actually lost a little wort when I put my lid on since it sits about .25 inchesintonthe kettle!
All in all a good day, I have 5.5 gallons of 1.064 beer in the fermenter and used no extact for the first time ever when brewing.