Benchmarks compiled and aggregated by tipster @_rogame indicate that AMD's new Smart Access Cache technology might not offer a game-changing performance uplift in most cases. Nevertheless, the same benchmarks indicate that Big Navi's raw raster performance could make that a moot point.
https://www.notebookcheck.net/AMD-s-Smart-Access-Cache-might-not-deliver-massive-performance-gains-but-Big-Navi-s-raw-raster-performance-could-compensate.501064.0.html