I think you should have fixed the one query that was the issue, since you already identified it as a problem.
instead you changed the entire server behavior to account for one bad query.
In my shop, we already have a maxdop set to 8 instead of the default of zero, because I'm under the impression that the combining of those more-than-8-parallel streams can often cost more to merge them together than a lower number of streams, so in general, i think 8 is a sweet spot.
what is double CPU for you? from 25 to 50 percent, or from 2 percent 4 percent?
i think details are going to be important here
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