Have you enabled LLC?
Set it at 50% and see if that smooths out your VDroop.
In some previous Asus BIOSs they had increments of 12.5%. Moving up and down a notch from 50% might also help smooth things out.
IIRC, there is also a slider adjustment in some versions of AMD OverDrive that might help --- called Over-Volt.
i have the NONE evo m5a97, which does have LLC but no control over the LLC %... i tried to look everywhere in the bios to set the LLC to different percentages but theres no option on the non evo version. so pretty much u either can turn on LLC or leave it sidabled... when i enable it i gettt wayyy to much vcore so. ill look into the amd overdrive overvolt thou