[engineering tangent]
"Nickel silver" (also called "German Silver") as used for frets is actually a brass. (Brasses are alloys of copper with zinc, and sometimes other metals.) Standard nickel silvers are 53-67% copper, 17-29% zinc, 11-20% nickel, and trace amounts of other metals. There are also leaded nickel silvers that contain 1% lead.
Scott, where did you get the "bell brass" frets from? Are they the yellow brass Dunlops, and were they described as being "the same alloy as Warwick uses?" I am surprised that they are so expensive.
In searching for info on "bell brass," all I have been able to find are are references to two bronzes that are used for casting bells. One is a tin bronze (Cu 80, Sn 19) and one is a silicon bronze (Cu 94, Mn 1-2, Si 3-5 plus traces), but neither of these are specified for extrusion, which is how frets are made. In fact, anything used to make a bell of any size would be casting material, which is generally not what would be used for extrusion - which calls the Warwick nomenclature into question.
Tungten AFAIK is too strong to be extruded. If you wanted a tungsten fret, you'd have to machine it, which would be tough and very expensive. Plus you'd need some very hard files for crowning.
Fret materials, like all thing, are a compromise. They generally need to be hard enough to stand up to wear from the strings, but not so hard that they can't be produced economically, and worked as necessary.
[/engineering tangent]
BTW Scott, I like your body designs, especially the SF-1 bass:
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