Classes are a safe default even if you expect things to go very, very fast.

The overhead of screwing up NUMA concerns vastly outstrips any kind of class vs struct differences. It's really one of the very last things you should be worrying about.

Allocating an array of a class vs an array of struct might seem like you're getting a wildly different memory arrangement, but from the perspective of space & time this distinction is mostly pointless. Where the information resides at any given moment is the most important thing (L1/L2/L3/DRAM/SSD/GPU/AWS). Its shape is largely irrelevant.