For 3X4GB the 'best' for sale are the Dominator CMT12GX3M3A2000C9 the best for 'performance : money' are the Dominator CMP12GX3M3A1600C9 which can be easily OC to 1800 MHz with a CAS drop to 8-8-8. Keep in mind, my answer is on OC'ing the RAM > Spec. Spec the The Kingston HyperX H20 2133MHz are the 'fastest' but no 4GB density.
However, I have no ideal how well they'll run on an ASRock X58 Extreme3. Meaning, 2000 MHz or higher is a bear to keep stable/error free. The i7 980X IMC craps-out about 2200 MHz, and you're going to need to increase the BCLK ~160 MHz or higher.
Tested ASRock X58 Extreme http://www2.corsair.com/configurator/product_results.aspx?id=1361988