Manual overclocking to 4.6GHz at 1.3V produced the biggest uplift in Cinebench R20, with a score of 9,062, which is even faster than 16-core, 32-thread 3950X manages. Just let that sink in a second: the improvements AMD has made to this chip make up for a difference of four cores compared to the previous generation. That's pretty impressive. Unfortunately the single core performance still suffers under this overclocking regime, and the performance dropped by seven percent to 594.
Perhaps per CCX or per core overclocking will change this after the fact. But, for now, it just isn't worth overclocking these chips.