We reached 4.2GHz with the G3258 we’re using for our tests. It's the second one we obtained after our first sample was unstable over 4GHz on any board I tried. My successful overclock was achieved with one manual setting: changing the CPU Ratio from Auto to 4200MHz. We did try the OC Genie and were a little disappointed that it did nothing.
Given that a few benchmarks showed lower results after the overclock, and since we could not record BIOS screen shots, we cannot rule out the possibility of some sort of firmware bug.