Nforce 4 A01 silicon not reliable at 5X
 

NVIDIA's SOON TO BE introduced flagship PCI Express Athlon chip at this stage won't offer you 1GHz Hypertransport.
Nvidia is very precise in its document that due to the number of electrical factors its chipset will refuse to run reliably at 5X Hypertransport speed

http://www.theinquirer.net/?article=18849