hi, i have the same ram, but i am running an eight gig set. I realized that my board didnt offer the implied support for ram e.g. its always 800 straight out, but im sure that ram is 2.3v and also id advise getting a or the newest bios flsh for your 750i , i have the same. if you have an 8 gig set up there may and probly is a bios flash for improved stability. The other issue is make sure all of them are seated. take them out and reseat the ram being sure that they are all in place. ive not been able to oc these much. im timid about cpu and memory ocs separatly. make sure you have enough file space on your hdd and ive consequently turned my vm off. the ram may actually be 800 ram that is overclocked, so maybe find another way to get it above 1066 with mobo select timings not expert and use youre cpu to up the ram value. ive had great luck with the lower latency in one or two cases overclocking nearly as high as you can get with a higher mhz ram 800 is like 1066. but i think if youre board can do it, hope you have the support for the faster ram or rather higher mhz. its ready for it. or just opt to overclock linked or synced. both are good choices and your ram wheather its factory oc or really 1066 will and should work optimally!