Here is the vdroop pencil mod for the P5K 'vanilla'. Mod should be the same for the DLX, but the BIOS option for 'CPU Voltage Damper' actually works for the DLX model, making this mod useless for those mobo's.
You need to pencil the resistor down, to achieve the 'minimal vcore droop'. So far the best results I have seen, show this mod to trim down the droop to ~.2-.25v at load.
Before you do the mod, please turn your whole cpu off, once unplugged, measure across the marked resistor and measure it Ohm resistance...then post back with the original value please.
I performed this mod on my P5B-dlx and it worked great! I have no vdroop below 1.55vcore...at all. I shaded the resistor to 7ohms...i believe the original value was close to 30ohms.