What angle should I set the VTA on my VPI turntable?

I agree that setting SRA should not be used as a tone control. There is just one correct setting. It’s like adjusting the play-back head of a tape recorder. The purists are correct, though, that it could be different for different record labels. A table of those differences has been published.

Here is the method I recommend: Find a recording that people say is good for hearing the differences when you adjust SRA. Do a search here and elsewhere; there are a lot of suggestions out there. If you can’t find one, take a record of a female singer and listen to it over and over ’till you know it very well. I have used Joni Mitchell’s "Blue." Make sure it’s something you like ’cause you’ll be listening to it a lot. Set your tone arm to absolutely level and listen to the recording a few times.

Read all you can about your cartridge and see if reviewers or users have a consensus suggesting tail up or down. Change the angle in that direction a very small amount and listen to the whole record. You are listening for the voice and instruments to "pop" making them more 3 dimensional. It’s subtle, but it’s there with the a stylus having a clear rake. Do that again and again in very small increments. If you do not hear improvement soon go back and stay at level.

If your reading does not come up with a tail up or down consensus. You may have to try this in both directions.
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An alternative method uses the recording Flying Fish HDS 701 if you can, find one in reasonably good shape. If you can do a search to see how to use it.

The "tone control" aspect is once again putting the focus on only the most gross, crude, entry-level aspect of VTA adjustment. The idea of adjusting according to some table of record thicknesses is equally fruitless. Either put in the time and effort to learn to hear what is going on, in which case you will almost certainly agree fine tuning is an art well worth mastering, or don’t in which case set it and forget it.

In any case you already have the one and only thing needed to perfectly fine tune VTA: your ears. 

At best it is always going to be compromise as record lathe cutter head angles can vary between manufacturers, then there's record thickness and finally VTF can impact cantilever angle.