Comments about how bright 3D is are subjective. We do not attempt to measure how much brightness is lost going from 2D to 3D, how much is lost by the active glasses (at minimum about 50% since one eye's shutter is open, when the other eye's is closed, or by various "glasses brightness" settings that many projectors offer. That last, isn't about the glasses themselves, but how long the projector outputs the image to one eye before it shuts off and works with the other eye. The brighter the setting, the brighter the image, but also the more visible the cross talk.
With most 3D content on the Pro Cinema 4030, I watch with the Glasses Brightness setting either in Low or Normal. I find too much crosstalk for me not to notice, when in the High setting which is the brightest. As a result, my comments are based on the middle setting.
Using 3D Dynamic with that setting, filling about 100" diagonal on my 1.3 gain screen in my theater, provides a reasonably bright image. Pushing out to the full 124" diagonal when I watch widescreen movies, however, is already getting about borderline. You wouldn't associate the term "bright" with it in any way.
Now switching to 3D Cinema is another story. Figure that 3D Cinema at 100" with the Pro Cinema 4030 is not quite as bright as 3D Dynamic on the 124" size. When I'm watching HDTV or a 16:9 movie in 3D even at 100" I'm often likely to choose 3D Dynamic, although 3D Cinema is definitely borderline acceptable. It's still brighter than all but a few other sub $5000 projectors and the ones that are, in that price range, are mostly low end home entertainment projectors which cannot begin to match the 4030's picture quality. That low end/entry level includes projectors like Epson's own 2030, the BenQ W1070, and a whole bunch of low cost Optoma projectors to give you a rough idea.
I do not like dim, whether 3D or 2D. Let me put it this way, in the last 10 outings to see 3D in the local cinemas, all but one was on IMAX screens. I go not because the screen is bigger, but because the IMAX 3D theaters are typically significantly brighter to dramatically brighter than some of the regular theaters 3D.
3D is one area where the more expensive UB series projectors have the advantage. They have about enough extra horsepower to do a screen 8-10" diagonal larger while maintaining brightness. Let's reword that to say that a UB projector can handle one size larger screen while delivering the same brightness.