Our copy of the Phenom II X4 980 happily overclocked by 500MHz, to 4.2GHz, at 1.5V—only a tenth of a volt above stock. When we tried to push further, our chip was a bit of a tease. It would POST and boot into Windows without complaint at 4.4GHz, but one of the four cores consistently threw an error in our Prime95 torture test. We tried incrementally cranking up the voltage, all the way to 1.65V, but that didn't help. Despite a tantalizing glimpse at 4.4GHz, we had to settle for 4.2.
The additional 500MHz improves the X4 980's performance to the point where it gives the Core i5-2400 a true challenge—but the Phenom needs the help of overclocking to get there. Even with the frequency boost, you'd still be better off in most of these apps (which are nicely parallelized) armed with the two additional cores of the Phenom II X6 1075T.