>The biggest consideration which I know of, and have seen on here many many
>times, is the throughput capability of a Linux server. Your main thought
>here is not so much how many PCI slots are available but how many pci buses
>are available, as this is where your internal I/O limitations fall into
>place.
...

Well said, Andy.  With today's high-intensity I/O cards, the PCI bus has
become a notorious bottleneck for sever implementations, necessitating multiple
(split) bus approaches to compensate, and whole new paradigms like InfiniBand
to avoid bus issues entirely.  Bus capacity is often overlooked in server
planning, and can be a (mysterious) show-stopper.

  Richard Sims