Any lesser known knobs one should know? I'm considering a .NET backend for my compiler

If on Windows, one is to see what C++/CLI would generate, with ildisam or similar tool.

You can also emit MSIL for what you actually want to do, with low-level bytecodes.

Then there is unsafe, ref structs, stack allocation, fixed buffers, scoped types, manual memory management, array pools, memory pipelines, the various span variants.