Intel has been pretty tight lipped about the some of the details of its higher end Skylake-X processors that are on tap, though it let slip some additional information about its Core i9-7920X CPU. As part of an update to its processor price list (PDF) for mid-July, Intel revealed that the 7920X will have a base clock of 2.9GHz and 16.5MB of cache.
The Core i9-7920X is a 12-core part with 24 threads. It's not uncommon for CPUs with more cores and threads to have lower clockspeeds than less expensive models with with fewer cores and threads, though a look around the web shows there is some concern over the relatively low 2.9GHz base clock on this one.
Sitting one rung lower on the Skylake-X ladder is the Core i9-7900X, a 10-core chip with 20 threads with a 3.3GHz base clock and 13.75MB of cache. And compared to AMD's Threadripper 1920X, the Core i9-7900X is 600MHz slower. Should we be concerned? It's too early to tell, but there's a lot more to consider beyond the base clockspeed.
Our own Jarred Walton notes that the base clock on Skylake-X is practically meaningless. The base clock boils down to the 'guaranteed' clockspeed that users can expect, on all cores. The thing is, the Core i9-7900X has a base clock of 3.3GHz, but the all-core Turbo Boost 2.0 clock is actually 4.0GHz. Every motherboard we've tested the Core i9-7900X on has been able to hit that speed with no fuss, and some will clock it as high as 4.5GHz on stock 'Auto' settings.
What this means is that while the base clock on the Core i9-7920X is relatively low, it's the all-core Turbo clock that we are more interested in. Our guess is that it will be around 3.7-3.8GHz or thereabouts. And of course the i9-7920X is still an unlocked enthusiast chip, so overclocking (with adequate cooling) should eliminate most of the clockspeed deficit relative to other Intel parts.
All of this will only matter for enthusiasts looking to piece together a meaty system with a whole bunch of cores and threads. For gaming, the Core i9-7920X will be overkill anyway, no matter the Turbo clockspeed ends up being.