Is your RAM linked to your CPU FSB or are you upping them separatley? Only thing I can think of is that your RAM isn't keeping up to the speed of your CPU. Need to know speed, timings and voltage. Don't raise the vcore any higher. 1.45 is plenty for 2.8GHz.
I wouldnt go over 2.1 volts on the memory. Not sure what the gskills are rated at, but 2.2 is probably the absolute max for most ddr2 memory.
actually, a lot of ram is rated for 2.2, especially if its high performance, 2.2 is usually the max you see