The number of editors really isn't to the point: I'm sure there is some hidden assumption there (some theory that makes it relevant), but I can't figure out what it is. There are a handful of editors that are seemingly "full-time" by normal business standards, hundreds that log in on any particular day, and several thousand that are "active" (depending on your definition of active.) It's your usual inverse logarithmic curve, of course. But the "backlog" would be exactly the same if it were one super-robot reviewing 8000 sites a day, or 56000 editors each reviewing one site a week.
But the other numbers are problematic. We don't track number of submittals processed -- it's about the same as the number of submittals added (because the total number of submittals stays in the .5-1M range). But that has nothing to do with the number of sites reviewed, since many unsubmitted sites are considered (and not listed); also, many submittals are obviously spam (and not seriously considered.) Common-sense triage means that of unsubmitted sites, the best should be reviewed first; while of submitted sites, it's more efficient to handle the obvious spam first. And the longer a site waits for a review, the longer it's likely to wait more for a review.
All of which doesn't have any obvious closed-form solution, and giving numbers to someone who thinks there IS a closed-form solution is a cruel, cynical kind of deception in itself.
One number is obvious enough -- the average category gets updated (at most) once every six to twelve months. We don't know whether there are any "average" categories, but that should at least suggest what kind of expectation for time-from-submittal-to-review would be reasonable. (If it will be, on average, 6 months from the submittal date till the next time the category is CHANGED, then obviously it's brain-dead and insane to expect a site to be listed in an average of LESS than 6 months! And you can't even get a statistical handle on how much longer it would have to be, unless you know the percentage of spam submittals in that category. But perhaps that percentage you could get from Googling research.