I believe the 1.6 gain for the HP with the geometry you used would be for the viewing position centered with the screen. If you move perhaps 3 ft. to the right or left of center that will probabaly drop to something like 1.3.
For 2D viewing you will find that any screen with a gain of even 1.0 will be adequately bright on a 114" screen, when used in a fully light controlled home theater. So for 2D you have a lot of choices for a fixed frame screen ranging from the low cost models, such as from Elite, to moderated priced models from Carada and Dalite. However, it you are looking for a screen that will give you a boost in brightness for 3D viewing then you can either go with an inherently high gain screen or one with moderate gain that also retains a significant amount of the polarization of the projected light. Unfortunately this whole area of 3D and polarization retension is very new and most manufacturers have not ideal how there screen materials perform as far as retaining polarized light. So for now we only know how screens perform in this regard based on tests being performed by AVS members and thus we do not have a comprehensive list of which screen materials actually maintain significant levels of polarization. Also if you look at the list of screen materials and the test results in Post #1 of this thread you need to realize that some of those materials are only sold with roll-down screens while other are only sold on fixed frame screens. As far as the Dalite fixed frame screens are concerned, in addition to the high power fabric you mention above, the Cinema Vision is a viable alternative in the angluar reflective category. While not as high quality overall as the more expensive Stewart Studiotek 130, the DaLite Cinema Vision fabric can be purchased with several different models of Dalite frames, starting with their budget Perm-Wall series and moving up to their higher quality (and better looking) Cinema Contour series. While the actual gain of the Cinema Vision appears to be a little lower than the rated 1.3 gain, it does maintain quite a lot of the polarization of the projected light and will give you a boost in brightness for 3D viewing if you use a JVC projector in combination with JVC 3D shutter glasses (i.e., but don't use the Xpand glasses which have the opposite polarization). The AVS store sells DaLite screens, so I suggest you give Mark a call to see what he can do for you, or to see if he has any other suggestions.