Q: 64-bit PCI - 66 Mhz vs 33 Mhz networking performance?

[Brian]

Hi everyone,

  I'm currently looking into the Tyan Thunder dual-K7 board, and I'm
pretty sure it's only equipped with the 33 Mhz variety of the 64-bit PCI
slot.  Does anyone have any real-world performance information on the
difference one could expect with the 66 Mhz over the 33 Mhz?

[Note: Microway's website, for their Beowulf Cluster, mentions that two of
 the slots ARE 66Mhz, but Tyan's website seems to say otherwise.  Anybody
 using the boards know for sure?]

  In other words, should we wait for a board with a 66 Mhz bus?

  Originally I was thinking of the difference with Myrinet, but since I'm
not yet sure what our network requirements will be, any advice is more
than welcome.  How do multi-port ethernet cards on those slots fare?  Or
gigabit e'net?

  Thanks for any info,
  - Brian