Microsoft corporate VP Marc Whitten broke the news during a podcast with Major Nelson (take a listen here) saying:
This is the time where we’ve gone from the theory of how the hardware works–what do we think the yield is going to look like, what is the thermal envelope, how do things come together–to really having them in our hands. That’s the time where you start tweaking the knobs. Either your theory was right dead on, or you were a little too conservative, or you were a little too aggressive. It’s actually been really good news for us, and an example of that is we’ve tweaked up the clock speed on our GPU from 800MHz to 853MHz.
In terms of real world performance, the 53MHz might equate to a couple of extra frames per second. Nothing mindblowing, but certainly welcome nonetheless.
There was no official word on a rumored increase of RAM on the Xbox One from 8GB to 12GB though. In fact, we think that this “rumor” is complete rubbish. The increase is unlikely to make that much difference in terms of actual gaming, and assuming Microsoft want to actually have consoles manufactured and available to the masses come November, it would be impossible to pull off.