Well, it's not that surprising. 5800X has 8 cores but within a single CCX, in simple terms it means that all 8 cores are in a single cluster, so they all share the same cache, they can switch context(threads) very very quickly with minimal penalty. The 5900X has 12 cores, but in two 6 core clusters instead. There is a connection between the two clusters, but it slows down any kind of cross-core, cross-thread communication if those threads don't run on the same cluster. Since games generally won't be aware of the CPU architecture, they could be getting penalized for this communication between clusters and end up being slower. This is not exactly new. The 5900X is still going to be much faster in situation where cross-cluster context switching doesn't happen very often, or where threads don't share cache data. It's highly situational basically.