The A13's high-performance cores are shown running at 2.66 GHz in today's result, compared to 2.49 GHz in the A12, leading to an approximately 12–13 percent gain in single-core performance for the A13 with a score of 5415, compared to an average 4796 for the A12 in the iPhone XR.
Interestingly, the A13's multi-core score of 11294 is nearly identical to the A12's average score of 11192, although Geekbench's developer John Poole tells us there could be some throttling due to thermal limits as similar situations have been seen with the A12 in the iPhone XS and XR, so we may have to wait for more data to see where the A13 truly tops out.