As one of the five close voters I've chosen Too Localized because of this part of the close reason:
... an extraordinarily narrow situation that is not generally applicable to the worldwide audience ...
Tweaking the priority settings on processes is something that works or breaks depending on your usage scenario, you have left out what your usage scenario is (for privacy reasons) but if you would have given it it would be different from many others.
If you would have accepted one answer over the other, it would have not applied to the general audience. Simply because different programs can result in a different scheduling of your processes. When you defer from the general standards, you get something that only works for your use case rather than something that applies to the general audience. As Ivo Flipse outlines in his first comment to your question, there are no urban legends that would apply to anyone; simply because they would have already been applied after these many years...
Furthermore, as this is a question where both ends are pulling; I would otherwise have chosen to vote your question as not constructive, for similar reasoning as provided above. There is no definitive answer.
I see no way to improve your question. It boils down to doing some homework / research on how to improve the performance of these programs in your use cases. Do performance comparisons before and after applying your tweaks to see what works and what doesn't. Also check out whether you can get around running things from RAM instead of your HDD where possible; similarly, database programs allow you to configure caching which also helps improve performance.
The bottom line here is: There is no single magic fix that works for every program on every PC.
eg. I do not run a virus scanner, while a relative of me needs a virus scanner and a firewall to be safe...