Without having a JVC RS25 here, my take is that the RS25, like my RS20 will only have a slight black level advantage over the Runco. The Runco image definitely has more pop than the other two projectors, which to me, more than compensates in this case. Note, the blacks on the Runco look blacker than the RS25 below it, but also note that the RS25 image is definitely the more overexposed of the two. The easiest way to tell is to look at the pause marker in the lower right. See how it's more blurred on the RS25. From much back and forth between my RS20 and the Runco, yes, the RS20 (and therefore the RS25) does do a blacker black on this scene (ok, all scenes) than the LS-7. That they are close enough that I need to clarify, is good indication that the LS-7 is where it needs to be, a first class - ultra-high contrast projector capable of excellent black levels, based on DLP chips and a dynamic irs.
Below are two more dark scenes comparing the Runco (right) and Epson (left) from Space Cowboys. Why compared to a roughly $3000 projector? Easy, two reasons. At the moment, besides the LS-7, I have several other projectors here, but, the two best are my own JVC RS20, and the Epson 9500UB. The JVC is better than the Epson (and doesn't use an iris), but the Epson's black levels are still better than most projectors selling for under $10,000. More to the point, the two are fairly comparable in terms of black levels. Overall, my RS20 should do slightly better than the Runco, on most scenes (no iris), but truth is, it sits up high on it's shelf and I rarely ever bring it down to take into the testing room (only once since I installed it).
Below our usual two images from space cowboys. This shows the effect of the iris action. If you look closely at the first image, the two projectors are pretty even in brightness (the planet looks a touch brighter on the Runco (left), but the pause bar (of the PS3) in the lower left, would indicate that the Epson is a touch more overexposed. Certainly the Runco, though, looks a little brighter, withbrighter starts but similar blacks for space. On the lower image, though, where the iris is mostly open, the Runco's space, is darker and the starts stand out more.
This is typical when comparing dynamic irises. With two projectors that are otherwise close in black levels it's quite possible, if not likely that at some points in terms of the brightness of scenes, that one projector may do better blacks on one type of scene, and then the other projector may do better on a similar but slightly brighter or darker scene.