From what I've read, 2.4 or 2.5 is about the peak output of the HP screen, but in reality, we might get somewhere between 1.8 and 2.0 gain.
Also, with the 133" scope screen, the image will be over scanned (zoomed in) so it is the equivalent of a 140" 16:9 screen.
Most reviews show about 700-800 calibrated lumens when brand new with the X35. With that amount of gain, we plan to use low lamp mode and close the manual iris a fair bit to reduce brightness and improve contrast ratio. If my calculations are correct we should be in the 20 FtL ballpark.
However, when we mask the screen to 105" for 16:9, over-brightness might be more of a problem, but hopefully low-lamp and the iris will manage that.
Of course, over time the bulb will dim, but hopefully with this screen, we will get more out of it.