Stability towards what? Processor overclocking or memory overclocking? If the latter, the highest memory overclocking advertised is on the ASRock board while the Gigabyte board seems to have a better power delivery towards the CPU.
They both are the same, I wouldn't overclock on those boards, apart from mildly on both processor and memory(DDR-3200MHz) and leave them alone. Be sure to buy a reliable PSU for your build.