it's interesting to note that the Voodoo 3 takes advantage of all AGP 2x features except AGP texturing (and probably a few that I don't know about), however the V5 can't, becuase in order to run Dual chips on the one card, they had to do some tricky work. They could not run the Voodoo 5 in AGP 2x, mode, rather it runs as if it was a 66mhz PCI bus.
what this means is that when playing games that aren't dependant on the video card, the limitation will either be the interface (using AGP as a PCI66), or the CPU, whereas when the Voodoo 3 isn't being the limitation in a game, it is most likely the CPU (it can be the bus as well, but it's alot less likely).
What this all boils down to is this, the higher your FSB goes, the higher mhz your AGP port runs at. The Voodoo 5 would benefit from that, but you would only see the performance increase when the card isn't the limit..