This SIM2 is designed as a home theater only projector. The 3D-2 looks good in 3D up to about 100" diagonal, in terms of brightness. The point is, you can enjoy 3D on an smaller sized screen - say - 82" and 100" diagonal, and have respectable brightness while your lamp is fairly new, with a traditional screen surface, or go a bit larger with higher gain screens. Ultimately, though if you want to take advantage of the 120" diagonal or slightly larger traditional screens the 3D-2 can handle in 2D, you will be a bit starved for lumens trying 3D at that size. I certainly felt that way when I tried to put a Cinemascope shaped movie up to fill my 124" 2.35:1 screen.
I couldn't watch the 3D for very long before I zoomed out to a smaller size. Of course some folks demand less lumens to be happy in 3D, remember, you are giving up about 3/4 the brightness when you kick in 3D.
What that means, is even on a 100" diagonal screen, 3D won't be anywhere near as bright as 2D would be on a 120" diagonal.
If you want to go a bit larger, go with a higher gain screen. Still, I'm not a fan of screens with gains of, say higher than 1.8, and am most comfortable with 1.3 - 1.4 where the trade-offs are negligible. All of my comments - are subjective recommendations, based on my "regular screens" being 1.3 gain. Stewart Studiotek 130.
As I have offered in other conversations about 3D and brightness, in other reviews and articles; you could go with two screens.
In that case, perhaps a large, fixed wall screen with normal gain 1.0 - 1.4 for 2D. To handle 3D, or even 2D when you want really bright (sports with the lights on), consider adding hi-gain, motorized screen for when you really need the brightness for 3D and intentional ambient light.
I'm one of the few folks with a two screen setup. With projectors like the SIM2, if I want a bright 100" diagonal 3D image I have to go to my brighter 3D screen (which soon will be replaced with a 2.5 gain screen, just to see how many issues that much gain brings to the party.)
Bottom line - the SIM2 has just enough brightness to give you a respectable one screen solution, on a smaller screen, or you can support larger screens by going to higher gain screens for your 3D viewing.
Plan B, if your room supports it - a high gain screen for 3D, and a really good screen without high gain, for normal 2D viewing.