A developer has created an app that can test the 60fps rendering capabilities of the S4 SIP, the processing platform found in the 4th-gen Apple Watch. He has reported that the watch equals the iPhone 6S in this test. The watch also used less than 70% of its processing power while running this app.
https://www.notebookcheck.net/Apple-Watch-4-found-to-be-just-as-fast-as-iPhone-6S-but-only-for-certain-metrics.337036.0.html