I don't know how fast the high end SANs go, but an EMC AX100 combo with QLogic cards managed 1/10th the bandwidth of a local SCSI disk, even using QLogic cards in pairs. I gauged this with a rather unscientific file copy test and the Performance Monitor on Windows Server.

I wouldn't want to keep my pagefile on a SAN volume at that rate, let alone my OS.

Are other SAN systems faster? Or am I running into a bottleneck with the fibre channel connection or Brocade switch, part of the combo? Sure the AX100 is only SATA, but that can't be the bottleneck by itself.