OCC has published a review on the ASUS M4A89GTD PRO/USB3 890GX Motherboard

I knew under water I could push the voltage a bit more, so I topped it at 1.5V and pushed the reference clock and multiplier a bit more and was able to boot at 4.3GHz but it was not stable enough to pass benchmarks so I tapped them down a bit and found a sweet spot at 4.226GHz, where everything ran stable and the temperatures were still low. For the final overclocking settings, the processor is at 4.226GHz (216.7MHz x 19.5) at 1.5V and the memory was set at 1733MHz with timings of 7-7-7-20.

ASUS M4A89GTD PRO/USB3 890GX Motherboard Review