@herman - is your screen 120" diagonal? or 120" wide? If it's 120" diagonal, the actual width is only 105" (8-3/4 feet).
Also, I specifically stated that mgould would need a much higher lumens if he was going to do a calibration (i.e. grayscale and color cube calibration using Lumagen Radiance -- which is highly recommended anyways). The calibration will reduce the max amount of light the projector can output. So, in essence, calibrating a 1000 lumens projector will essentially reduce it to something like 700 lumens (approximation).
In my room, if I don't do a grayscale/color calibration, I can certainly run my Sony 1000 lumens in "low light mode" and the brightness is just fine. However, when calibrated, I have to use the "high light mode" because there just isn't enough output in low light mode -- the picture is just washed out and there's no "pop" in the color.