on your AV8 try setting the agp pci lock to 74 mhz for the agp; most people say this allows them to over clock a lot higher (before spending money on a new board... In which case get the MSI K8N Neo2 or the EpoX 9NDA3+ or 3J, all 3 OC very well - there are no 939 agp DFI boards)
edit: saw you had a FX55, so i assume you are overclocking by changing the CPU multiplier, so i realise that you want a new board for higher voltages, and not higher "fsb" (HTT) speed..... Well, what voltage are you running your cpu at now?