E6600 OC hindered by CPU batch or MB?

that vcore is a pretty high, whats your northbridge at?
It might be the memory that is limiting you, I got the exact same memory, make sure you are running it at 5-5-5-15 at vcore 2.1v at first, it tends to be pretty picky, im not actually that impressed by it so far, gonna have to try some more settings with it though...

vMCH is at 1.6 (tried it at 1.65 but no diff)
VFSB termination is 1.40
vICH 1.20

In my experience, and according to posted overclocks, the P5W DH hits a wall at 400 clock, 1600 fsb with default voltages. So at this point don't increase any motherboard voltages. You might try the AMD technique, put the fsb up to that wall then put DOWN both the CPU multiplier and memory ratio, putting the memory under the rated speed if you can. Then, if the system runs, up the multiplier, memory ratio, and core voltage.

My P5W DH with an E6400 runs at 3.2 Ghz CPU on 8X multiplier and 1.515 vcore; 400 clock, 1600 fsb, and the memory at its rated 800. The motherboard voltages are default. The system is used 24/7 running the 64-bit Linux Folding@Home SMP client.