So I concluded my research. Results are as follows:
All sixpence coins sound pretty cool, however, the silver ones sound more balanced and less ‘metallic’ chirpy.
Titanium picks sound almost identical to the silver sixpence coins. 95% the same tone.
Some wooden picks (ebony, rosewood, etc) sound almost as bright and balanced as the silver picks. But 100% without the metallic chirp.
I’ve noticed that while I prefer the feel and sound of the silver coins/titanium picks, I get an unpleasant type of feedback through my amp when those coins/picks touch the strings. Further research identified that this feedback only occurs on my 1967 Epiphone and my LP with PAF pickups. These particular pickups happen to be unpotted.