PC Stats posted an Asus M2N32 WS Professional nForce 590 SLI Motherboard Review

For business applications which demand SCSI configurations, or professional grade network cards, the Asus M2N32 WS Professional has two PCI-X slots located just below the blue PCI Express x16 slot. Each 3.3V 64 bit PCI -X slot operates at 66 MHz, which means each can support a theoretical maximum bandwidth of 250MB/s. This works out to the same as a PCI Express x1 connection, but obviously the list of supported PCI-X devices is much more substantial than PCI Express x1 devices at this point in time.

Asus M2N32 WS Professional nForce 590 SLI Motherboard Review