Coulda made your own thread instead of necro'ing this one buddy (though, I admit its not that old anyways
Anyways, I also have an i5 and the CFX-SLI version t5xe.
3.9 @ 1.264vcore is my 24/7 config. Runs at 36-40C in a ~23C room.
Usually people report a 3.8 wall w/ an i5, but I suppose I got lucky with mine 100 mhz higher. I could NOT get to my 4.0 goal OCCT/Prime stable until I reached 1.4 vcore. 4.2ghz was the max I could get to staying at 1.4 while still remaining OCCT/Prime stable. Regardless, 4.2 @ 1.4vcore is also saved on my bios, but I personally don't think the big jump in vcore voltages warrants 100-300 extra mhz, hence why I'm at 3.9/1.264
Watch your VTT too. It'll start to get high with auto. After you're done reaching your goal (which I'm probably guessing is also about 4.0), start testing stability while lowering it.
EDIT: Forgot an important note, I use a hyper 212+ with 2 fans. I cannot help you with stock numbers.