Pushing it at -150c I only managed 6.4Ghz with enough stability to get a screenshotwith all cores.
Overclocking the Haswell CPU is pretty close to the same speeds obtainable by Ivy Bridge 3770K. The Haswell cold bugging at -118 with default settings and -150c tweaked out. With the latest bios I was able to recover quickly and boot into windows at 6Ghz.
I did notice some onboard GPU artifacting when the cpu was heavily overclocked. Most likely due to the memory running at high speeds. I did experience a few random scrambled screens while not running a bench program.
I experienced some issues with the early bios and custom memory settings so I ran XMP to run at 2666Mhz with stability. If I set XMP and then set manual to adjust speed with some success until you reboot. The Intel BIOS has the ability to modify secondary timing and sub timings but with the above limitations it was I struggled to get anything to run. I did test with 2666C11 Platinum's with the same behavior. Fixed with later bios update
As you can see from the screen shot above, the Haswell has an improved IMC. This result was done with SPD settings in BIOS with the exception of tRFC was set to 260. I reverted back to an older BIOS to see if I could adjust memory timing and I had inconsistent results that I discarded. I tested both 125 BCLK and 100BCLK to find they produce close the same results in AIDA64. fixed in later bios update
Running with the water cooling, I maxed out at 4.5Ghz with the ability to look Cinebench and 4.9Ghz for a screen shot in windows, on the memory controller I managed 2800Mhz with XMP timings.