Hi Eric,
The ES, IMO, is the single most significant feature upgrade Phase One ever offered past the 1 hour exposures on the old P45+.
The LS shutter works OK on wide to medium focal length, but for me the ES makes a huge difference for 75mm and up. Especially with the 240LS, where shutter shock or mirror vibration tend to create issues. I briefly tried the Mamiya 300, older lens, but much lighter than the 240LS, but on the 100, I had considerable issue with shutter shock/mirror shock, enough that working panos (which I do a lot of) was problematic as I never was able to get 4 in row with all the same focus quality.
The IQ100 still surprises me daily with just how much finer details can be perceived when it's used with good support, combined with the amazing DR, and it's a excellent platform.
My only issue is the mass and weight of both the XF and current Schneider lenses (80-40, 75-150 240LS) all of which constitute use of a tripod most of the time (at least for me). I still like the freedom of being able to hand hold and get low that a mirrorless solution offers or a DSLR with a tilting screen.
Paul Caldwell