I'm still no mathematologist, but it might be interesting to revisit the numbers from ten days ago. Specifically:
The ~300-and-a-little/day rate has held pretty steady overall, in that the GB hit 4000 right around the end of day 11, and 300 even would have taken 12 days. At the updated rate, with 15 days left, we'd expect to hit 9000 by the end with no extension -- and no bump of people joining later, no one doubling up, etc.
I'm sure there's some day-of-the-week variability, but it's perhaps interesting to note that today the rate looks to be around 500, which is a fair jump above the average. Perhaps the quickening begins?
(Edit: And I'm certainly no mathematologist, because I said 300x12 = 4000, when I was thinking of 333. The rest is probably maybe somewhat reasonable, though.)