I’ve gone as low as 1.0 qt/lb when needed. Makes a bit more of a pain to break up the dough-balls of grain, but just have to be diligent and make sure all the grain mixes in well.
With proper sparging I don’t think you should suffer too much in the way of lost efficiency though.
+1 to the above. I’ve done 1.0 qt/lb as well. Don’t know if I would go much lower, as it’s a VERY thick stir. If you’re worried about efficiency, you could double batch sparge.
The lowest I’ve gone was around 0.85 to 0.9 qt/lb. You couldn’t get all the grain wet with anything much lower than that. Maybe 0.8 qt/lb at best but that’s really really thick.
1qt for me is also as low as I have gone. +1 on the dough balls being more of a PIA. I have also filled my MT so full that it was difficult to stir without slopping some out. It is worth the work for a nice high gravity beer though.
Not sure if this is a help, but I use a cordless drill with a plastic paint paddle to stir mash. Mash is fully stirred in seconds. Double sparge is a good one, also adding extract to boil to bump gravity works.
Just .02 cents worth.