I would find a good stable with the ram at desired HT reference, ie HT-Ref 300. x 10 (you'll need this HT Ref to get 4ghz using 13.5 multi - it also gets you 1600mem). You'll have to lower the ram devider to get the 1600mhz for your ram. also lower the NB multi to 6.5 or 7 to get near 2000mhz effective speed. If the system is stable at these setting using the 300 HT Ref, then I would bring the multi up in steps until you reach 4ghz. Of course bring Voltage up as well. I was able to hit 4ghz benchable on the stock Heatsink and Fan this weekend. But I also have an Antec skeloton case that has a 250mm Cooling the entire board, I am sure this helped keep temps down.