Phoronix were recently given access to three servers running three different POWER9 Talos II configurations and compared them to EPYC and Xeon.  On paper these systems look amazing, thanks to the architecture supporting four threads per core; they tested  a dual 4-core Talos II system, a Talos II Lite with a single 22-core CPU and a Talos II with dual 18-core processors with thread counts of 32, 88, and 144 respectively. 

There were certainly usage scenarios where the dual 18 core system could outpace even the EPYC 7601 but could not surpass the dual Xeon Gold 6138 system.  The review covers a fair amount of benchmarks and configurations but doesn't begin to scratch the surface of wide variety of server configurations you need to consider before abandoning POWER9 altogether but the key metric, performance per dollar, shows these architecture solidly in the middle of the pack.

"Back in April we were able to run some IBM POWER9 benchmarks with remote access to the open-source friendly Talos II systems by Raptor Computer Systems. We were recently allowed remote access again to a few different configurations of this libre hardware with three different POWER9 processor combinations. Here are those latest benchmarks compared to Intel Xeon and AMD EPYC server processors."

Here are some more Processor articles from around the web:

Processors