Following up that last part -- I recompiled my x64 codebase with /volatileMetadata-, which reduced the volatile metadata by ~20K (the remainder most likely from the statically linked CRT). The profiling results were negligible, under noise level between the builds and both about 15-30% below the native ARM64 build.

The interesting part is when the compatibility settings for the executables are modified to change the default multi-core setting from Fast to Strict Multi-Core Operation. In that mode, the build without volatile metadata runs about 20% slower than the default build. That indicates that the x64 emulator may be taking some liberties with memory ordering by default. Note that while this application is multithreaded, the worker threads do little and it is very highly single thread bottlenecked.