I don't think there are any drivers available for any of the PCI Wireless Ethernet cards, only for the PCMCIA cards based on the right Prism chipset. So if you get a Mediator you're still stuck buying one of those wired to wireless bridges.
Not being particularly familiar with either the Permedia 2 (BVision) or Voodoo3 chipsets I can't speak to the actual 3d power of the two, but the BVision will definately give you better bandwidth from the processor/RAM to Video RAM than the Mediator + Voodoo will since with the Mediator all the data has to flow over the relatively slow Zorro bus first.
I wouldn't count on the G3/G4 cards. They may indeed show up when OS 4 is complete, but at the moment they would appear to be nothing but vapor. If they do come out, that would solve the bandwidth problem with the Voodoo card, but I wouldn't hold my breath.