I don't really understand what you're trying to get at, but the concurrency abstractions/safety in Rust is static, there's little-to-no dynamic cost over the raw C/C++ APIs. And, in fact, the checks mean that one can sometimes be more aggressive about what designs can be used, without risking weird runtime corruption.
this is probably a silly question because the content, though it might always be in RAM, will be branched to an order-of-magnitude less than it'll be used (once it's been loaded to cache)...but still, there should be an observable temporal-boundary to the context stored in cache and branch predictor in a procedural language, that would be manifest as an abstraction-boundary in a more parallelized environment