David: Recently I changed how I hold the pick. I was making a lot of noise, by my right hand palm rubbing on the strings. I figured out that I was rubbing them over the strings an inch or two to the left of the bridge, rather than muting at the bridge itself. The noise had been driving me crazy for some time, but I could not solve it. But I figured out it was due to how I held the pick, I tucked it in so much, that I could not play with my palm muting at the bridge, I had to move my right palm more to the left of the bridge, and the rubbing of my palm on the bass strings there made a lot of noise.
Anyway, I now don't curl my index finger back as much, and after this adjustment I am able to mute with my palm at the bridge rather than to the left of it, and it is much less noisy. I looked all over internet, and on this site, for examples of guys holding the pick. I do hold it a lot now like Gilbert, except that like you, my thumb nail extends more past the pick than with most I have seen. I think Yngwie is more like that, with much of his his thumb nail past the pick, rather than directly in back of it. You seem to extend your thumbnail even further past the pick than I do. I have heard others saying not to do that, but as I said Yngwie does it, and you do it even further I think. I find that it enables me to get pinch harmonics much easier doing that, and I can hold the pick securely in a more relaxed fashion.
I would like to hear your philosophy on how you hold the pick. Some say it is a matter of preference, but I don't buy in to that fully, as I said, I was holding it in a way that was causing me problems.