I can report that the T4 arrivals level security check point does indeed have a Precheck lane that was open at mid-day. To get to it upon exiting airside into the arrivals hall, turn immediate left and stay on the left side of the railing. Go past the Delta baggage re-check desks and the security check point is just beyond that. It was quieter than the upstairs check points, so much so that even on my return trip I chose to take the escalators down from the upper level, clear security then go back upstairs.

One little quirk of the Global Entry kiosk I discovered is that it takes your photo almost immediately as soon as you scan your passport, so all it got was the top of my head as I was fumbling with the passport. Of course, it wouldn’t let you try again, and I had to be diverted to the desks to be cleared by a CBP officer - who told me the speed of the camera taking the photo is a known issue - next time get glasses off and look straight at the camera even before sliding the passport into the scanner!