So the der8aur guy who make delidding kits posted a video of a delidded 7900X running all 10 cores at 5 GHz while running a compute-intensive workload (Prime 95 FFTs): https://www.youtube.com/watch?v=80sEZSODwpw
Apparently this sample was hitting 4.8 GHz even before he delidded it. Now, this chip was binned so there's no guarantee that most 7900X parts will run this fast, but he did mention that he expects delidded 7900X parts to average in the 4.6 to 4.7 GHz range with a good AIO cooler solution, which isn't too shabby.
Incidentally, at 1:55 in the video you see some stats on the screen and the core voltage is listed at 1.32V, which ain't bad for 5GHz either.