Nazu, try backing off in voltage and even cutting back to stock voltage to see how far you get.

Lithan is correct about adding more votlage increasing your temps.

Confirm you can do 266FSB on stock votlage first. This should be done with everything at stock votlage. There is no need to raise anything at this point and that includes the 840EE can do this speed with stock voltage (with the 14x mutliple).

Im not sure what your ram is made from, does it run @ 3-2-2-4? Elpida stuff doesnt like to run 3-2-2-4