The clock speeds I posted in my previous reply are just the
base clock speeds of each CPUs, i.e., 1900X at 3.8GHz, 1920X at 3.5GHz, and 1950X at 3.4GHz. Those are the
base frequencies at
all cores.
The
boost clock speeds of all Threadripper CPUs (as of this date) is up to 4.0GHz. Those are
boost frequencies at up to
four cores only.
All the aformentioned Threadripper CPUs also have full XFR (Extended Frequency Range) technology, which automatically allows an additional +200MHz (+0.2GHz) on the four cores' boost frequency to make the four-core 4.0GHz run at 4.2GHz, provided, sufficient cooling.
As far as
all-core boost is concerned, the 1920X can boost
all its 12 cores to 3.7GHz only; while the 1950X can boost
all its 16 cores to 3.6GHz only.
To give you an idea, here's an example graph of the Ryzen 7 CPU (not Threadripper, as I can't find a graph of such) showing how the base, boost, and XFR frequency works. Note that Threadripper CPUs are essentially two Ryzen 5 or 7 CPUs, so, for purposes of the Ryzen CPU graph below (a Ryzen 7 1800X), it only shows two cores can boost and only 100MHz for XFR (compared to four cores and 200MHz for TR CPUs).
More info on these here: https://www.custompcreview.com/wiki/xfr/
For the Intel i9 CPUs, the
base frequencies also pertains to
all cores, i.e., i9-7900X at 3.3GHz, and i9-7920X at 2.9GHz. The
boost clock speeds of both i9 CPUs is up to 4.3GHz but up to
two cores only. Similarly, the i9 CPUs also have a TBMT (Turbo Boost Max Technology) 3.0, which automatically allows an addition +100MHz to +200Mhz boost frequency on its 2 best performing cores. The i9-7900X can do 4.5GHz (i.e., +0.2GHz above boost) while the i9-7920X can do 4.4GHz (i.e., 0.1GHz above boost).
As far as
all-core boost is concerned, the i9-7900X can boost
all its 10 cores to 4.0GHz only; while the i9-7920X can boost
all its 12 cores to 3.8GHz only.
More info here:
https://en.wikichip.org/wiki/intel/core_i9/i9-7900x
https://en.wikichip.org/wiki/intel/core_i9/i9-7920x