Thanks for keeping us posted. How did you manage with your efficiency on this wort addition? Did you sparge at all?
I just did my first high-gravity brew a couple of weeks ago and I was surprised to see that I was right in my usual efficiency ballpark even though my mash was on the thicker side (for BIAB at least - 1.82 qt/lb). I don't have a refractometer, so I don't know my preboil gravity, but after my usual 90-minute boil I got a 1.110 wort.
I seem to hear "well, I don't know how well BIAB would work for a high-gravity beer" a lot, but it didn't seem to really affect my efficiency. I don't have my system 100% dialed in yet, so take this with a grain of salt, but I won't hesitate to brew barleyines/IIPAs/Quads/etc with my current setup going forward.