In single-threaded testing the Ryzen 9 3900X scored an average score of 519 over three runs, with multi-threaded scores averaging 7039. Performance was higher with the X570 ACE in this test, with an average single-thread score of 529 and multi-thread average score of 7106. In 3DMark the overall/GPU/CPU scoring breakdown was 11191/11066/11963, and with the same CPU/GPU combo on the X570 platform we saw scores of 10974/10866/11634.
Geekbench 5.1 average overall scores with the B550 Taichi were 1335 single, 11215 multi. This B550 test system should have an advantage with low-latency CL14 memory vs. the 16-18-18-36 kit used in the X570 ACE results in an overall test like Geekbench, with the latter providing average scores of 1341 single, 11191 multi. Higher single-core, and lower multi-core results, but not by much in either direction (again, tests run using different AGESA versions).
We could go through more tests, and more back and forth results, but in the end these platforms offered CPU performance within about 1% of each other. Features and price will naturally be more important considerations when comparing X570 vs. B550. However, I was interested in the internal/external storage performance with this B500 Taichi board, and to this end we ran speed tests using the fastest options we had on hand.