This is a rather unique item. I have no use for it, but maybe you run HP-UX, Tru64, Linux or whatever and want to give it a go!
I have three Quadrics SC40 QM-400 Élan (QsNet) network adapters, to be installed in PCI-X slots. Or, actually, supercomputer-interconnects. Quadrics used to be of the now-defunct Alenia. (AleniaAeronautica was an aerospace/navy subsidiary of the defense giant Finmeccanica).
These are, as you may've guessed from the above description, high-end networking and clustering interconnects and they support speeds up to ~3 gigabit (i.e. 320 megabytes per seconde). That should be about three times faster than regular gigabit ethernet. Information is scarce, however, but I know this much: HP Integrity rx2600 was qualified for these adapters, HP-UX, Tru64 and Linux all provide(d) support. Don't ask me how though. I once had the impression that VMS would support these as well, but I was mistaken and that's how I ended up with them.
With two nodes there's no switch necessary. The physical ‘link’ or interconnect, cable-wise, is simply an HD50M-HD50M. Beware though, as is written on the PCI shield, it's not SCSI. You know what? If you're interested two, you get one extra for free. (You can keep that as a spare or sell it on.)