I sit 2-2.5' from my 28" monitors, I'd obviously sit further from a projector. However I would not even want a single 47" screen, let alone 120", because I want to be surrounded. It's not just about size, and for me there's such a thing as to big.

The other downfall of a projector is space. Sure, I could use a projector, set up 3 of them, 3 angled backdrops, but it would take up an unbelievably large amount of space. I have a single 6'x8' L shaped desk that I wheel into the corner of with my monitors surrounding me. That's my immersive experience. It's RIGHT THERE. And I have noticed stuff moving to my left and right, I can spot people or monsters better, so it is giving an advantage.