The HD1000U can do 126" wide with no problem, so 120" diagonal is a piece of cake. Even my 600 Lumen 4805 does 126" wide very brightly with no problem on my pale grey wall.
Most likely it won't work well. Convergence will be really tough, especially without lens shift.
2.0 gain screen basically equals two HD1000Us compared to one HD1000U on a 1.0 gain matte white screen, so it would be sort of dumb to spend a $900 more for another HD1000U to get the same result (unless you want to run two on a 2.0 gain screen for 4x the brightness.
, especially since two lamps would cost about $700-$800. No thanks.
Make a curved screen with PearlBrite Material and you'll essentially have 3 HD1000Us compared to one HD1000U on 1.0 gain white screen.
Here's my 600 lumen 4805 on my pale grey wall in a room with one shaded light on (even though it doesn't look like it I could read a book in the room comfortably):
Forgive the grain it's from my camcorder which is poor in low light (I actually had to blur the image a bit to get rid of some of the nasty grain). The actual image was FAR FAR superior and brighter. This is in low lamp mode. I forget the image size, but there is a broom in the shot for reference. If it looks too dark raise your gamma or brightness for dark detail: