interesting stuff! I agree there was a definite difference in tone.
Two things that spring to mind. Stone is harder than metal. That's why it's used to polish or hone. At the end of your demo you did an exaggerated strumming motion, and I felt like it could really hear the pick itself on the strings. Also, if someone uses coated strings I'd think the coating would be gone pretty quickly, and perhaps it could even wear on the metal itself????
Your timing is great, I've been messing with different picks a lot lately. I have an acoustic which is really aimed more at fingerstyle, and seems to have more character when played with a thinner (.060 to .080) pick. Like you, I just don't like the floppyness, and you lose a lot of volume, I feel.(but the sounds are beautiful) I've been trying to find a sweet spot, getting as heavy as I can and still get a nice sound, (what i need is a good rosewood dread...but that's out of the question right now)
On the electric side, I recently bought a jazz pick, which is closer to the size of a dime as a standard pick is closer to the size of a quarter, and VERY thick. I'm guessing the effect is similar to the v-picks, which I've not tried. I love the impact of the jazz pick, soooooo smooth coming off the strings, really able to move faster, but soooo hard to hold onto!
I amazed that picks can be such a variable to begin with. I guess that's my point!
And nice playing! What kind of guitar is that?