I am curious - about how many k/n pairs remain in the range 10 million to 20 million, now that only 8 k remain? At the beginning of this project, the number of tests in a given range exceeded the number of GIMPS candidates, but I suspect that has changed now. If GIMPS was able to eliminate 60% of possible candidates by factoring, they should have had to do around 240,000 to 250,000 primality tests in the range 10M to 20M. At this point, I would not expect sieving and factoring to eliminate more than 1-3% of the remaining SoB tests, so we should be able to get a good idea of the relative density of candidates now.