I use slinky (0.009 high E) strings on my standard tuning guitars, and will probably use a light cauge (0.010 high E) when I get my dedicated
slide guitar. But I have to disagree with the idea that thinner strings sound the same as thicker strings. I would imagine that it is a basic principle of physics that the increased mass of thicker strings would have richer harmonic content (especially in the first four or five harmonics).
I wonder if that's true, it seems like it should be.
As to SRV, I had always thought that, like Hendrix and T. Bone Walker (I think?), SRV tunned down to E flat. Is that true?