The problem is not the mobo or the bios....
The problem exists on all makes of i865/75 mobo's and it has to do with the fact that your P4C runs an effective default FSB of 800mhz....That's a damn high FSB even at standard settings not to mention overclocked settings, and the problem is made worse when you consider that you're trying to run the sticks in duel channel, two sticks of ram living on the edge don't like sharing bandwidth at the best of times....
It appears different makes of mobo's like different brands of ram. One make of mobo may like Corsair but not Kingmax, while another make may 'love' kingmax but not corsair....Take a look around the various overclocking forums - You'll see problems with ram stability everywhere. May have something to do with the fact that DDR400 or PC3200 and above isn't 'officially' recognised yet, it's purely overclockers ram, or so i'm told.
The fix is to either 'up' your vdimm in the bios until your memory is stable or swap your sticks of ram for a different make. Just as a note, the problem also seems worse when running two 512k and above sticks of ram - Two 256k sticks in duel channel don't seem to exhibit the same instability problems, in my opinion the best setup for an overclocker in terms of stability vs peformance is 2 X 256MB sticks of ram in duel channel....As the reality is that at the end of the day, unless you're into a lot of photoshopping, there isn't an application on the planet that 'really' needs above 512MB of system ram.
Personally i'm using 2 X Corsair XMS XTreme ram PC3200 CAS2 and it runs in my Gigabyte 8KNXP no worries at all, although, naturally when the system is running any speed over default the vdimm needs to be increased in order to aid stability.
More and more i'm noticing that successful P4C overclocking has to do with vdimm adjustments rather that vcore adjustments....