What timings are you using on your RAM? If 4-4-4-12'ish, loosen it to 5-5-5-15. Should get you some more room to play. Unfortunately the P35 chipset (nor any recent intel chipset) doesn't allow CPU : DRAM ratios < 1:1. Don't forget to raise your MCH voltage to help it cope with the extra strain of four sticks. If it's not your RAM, that's likely the culprit.