The Geekbench single and multi-core tests reveal minimal gains compared to the non-Plus Snapdragon 855, but the GPU performance is not taken into account, so for a true comparison between the two SoC versions we will most likely have to wait for AnTuTu tests.
https://www.notebookcheck.net/Asus-ROG-Phone-2-Geekbench-results-reveal-Snapdragon-855-Plus-CPU-performance.427759.0.html