Joe,

Thanks for your analysis. I actually did try to edit the .dat myself, but it crashed. Further reading indicates I might not be using v0.39, so I'll try that again. It just made me even more hesitant to use a "non-standard" .dat. If I can make the .dat edits with v0.39, I'll continue the range from 300k, then move to 1M-20M on my next range.

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Keroberts1,

I'm not sure, but I would think that as the length of each of the tests runs longer and requires more blocks to process, the chances of a computational error goes up. I think GIMPS had a false positive before their most recent success, and that they end up needing a third tie-breaking test on a small but significant number of exponents. So I think sieving from 1M is still definitely worth it for such a small penalty.