There's a couple of good articles comparing copper bulletplugs to copper/silver WBT nextgens.http://www.tnt-audio.com/accessories...nextgen_e.htmlhttp://188.8.131.52/search?q=cache:...nk&cd=37&gl=us
IMO WBT Nextgens are priced unreasonably too high, especially silvers. The Silver WBT's do sound darn good, though
Copper bulletplugs are a very good place to start for DIY'ers at a reasonable cost. It doesn't commit sins of commision such as etched highs, hard upper-mids, etc.
Silver bulletplugs are better IME, but I would only spend the extra $ if you were making IC's using pure silver wires to maximize the benefit.
Personally, all these "low-mass" school of connectors share a distinct sound-character, and I wouldn't be surprised if many preferred the "high-mass" school sound, such as Vampire 800C, Xhadow, Bocchino, or even the older WBT Toplines.