Because it runs headless, and I don't really monitor its performance that closely outside of heat, I don't have any valid data to say it hits 4.2ghz. Likely not though based on the role as a media server.
At 100% load I see at max 68-70c
The case is awesome. I am really happy with the choice. Highly recommend for a small footprint build.
Been running it since Tuesday in its designed location in the living room, and it is VERY quite. You have to get basically right on top of it to even hear the fans, let alone any hard drives spinning.
From what I understand, and I have not validated this myself yet by observation, but it has a boost clock of 4.2GHz . I am told that is only on 1 core, and when all cores are maxed out it is lower, I've heard around 3.9GHz.