Thanks for the write-up. Many things to consider indeed.
I'm new to this world and site, and working on planning an entertainment room, that is somewhat small 10-11 feet by 14. The idea is to have a screen recessed in the ceiling, to hide the TV when we want to watch a movie or sporting event. With only 7' of room to the where the ceiling will be (older homes were not as big as today), I have narrowed down the screen choices to either 110" or 120". the latter may be covered the entire back wall, which would block speakers, while the 110" would provide more flexibility there, and may be plenty with a 12' viewing distance.
For the projectors, I have been looking primarily at BenQ, due to the good reviews and options, so with needing about 10' for either 110" or 120", I have been thinking about building a shelf into the back wall (2-3 feet wide), about a foot from the ceiling, and above the seats, which would allow me to move the projector freely to address any horizontal shifting needed. I understand I would need to place the projector upside down regardless, is if it were ceiling-mounted, so have to figure out some way to keep it stable while upside down. I could create something simple, or use some rubber stoppers for it to rest on stable. The advantage of using a shelf is the flexibility to move it around, and then the vertical lens shift could be used to make sure the right area of the screen is hit. A possible disadvantage would be that once the shelf is built, there is no adjustment up or down, as with a possible mount. Just entertaining this idea, as finding an appropriate mount, close to the ceiling is not always evident.
I saw you mention that the BenQ HT2050 only had 2.5% shift while their site claims 10%. Same for the HT3050. The HT4050 has 2.5% horizontal and 12.5% vertical. The latter is about twice the cost however of the 2050, so when considering budget, that would cover more than a good set of 5.1 speakers. The HT3050 may be the sweet spot in the middle depending on the improvements it may have over the HT2050. Still doing homework there.