These are my settings.  Go to Wiki for details of each, or just the web. 
- Interrupt 19 Capture  [disable]
 
In Nortbridge Configuration : >> Really “PCI Express Configuration: “
- Relaxed Ordering  [Auto]
- Extended Tag Field [Auto]
- No Snoop [Auto]
- Maximum read Request Size [4096 Bytes]
- Active State Power Management [Disable][
- Extended Synch [Auto]
 
In frequency/voltage Control
- DRAM Margin Ranks [Disable]
- MPS and ACPI MADT Ordering [Modern Ordering]  (for XP or later OSs)
- MAX CPUID Value Limit [Enabled]   > Disable for XP
- A20M [Disabled]
- Clockgen Switch Mode [Disable]  > this synch all clocks on boot, but causes the “double boot”  
- MCH Strap [Auto]