Everything about this run is the fastest a human has ever done it up to this point in history. darbian has held and improved the WR since October 18th of last year, starting with a
4:57.627 (only a few frames faster than the old record, which stood for a year and a half.) He again improved the record on January 14th, 2016 by 12 frames to a time of
4:57.427.And now, tonight, on an otherwise normal night (like all the others), he broke the world record once again! I'm very happy to say I was in chat to witness it this time and it was very exhilarating. You just never know when these sorts of things are going to happen (he had actually reluctantly decided to stream that night while waiting for his laundry to dry).
More info on running SMB can be found by tracing darbian's post history on reddit, especially his contributions to the WR submissions on r/speedrun, which I have linked in the URLs for the times above.
Here's the post for the new record.