Sean, this question has been answered several times on this forum. The quickest and simplest answer is there is no specific chart to compare how many accounts you can fit on a specific configuration as it depends on how big the sites are, whether they are static or dynamic, how much resources each site takes etc.
If I were to estimate for the above configuration I would say anywhere from 300+ accounts depending on the above criteria I mentioned. Good luck!
Oh that's a given, with specs like that you'd be able to host quite a bit, and have no issues, as long as the admin manages it well set's things up right etc, but wow with specs like that you could run tons!
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