I imagine that if you compiled an idiomatic program in a language like this down to machine code, the result would actually look quite different from assembly generated for an idiomatic imperative program for the same task. For instance, even if you optimised your compiler to keep the top of the stack in registers as often as possible, the "calling conventions" of your functions would be all over the place.

At the same time, presumably, common processor architectures have all undergone decades of targeted optimisation to improve their performance on the typical imperative code that is encountered in system and user programs. What are the implications of this? Should we expect a theoretical cap on the real-world performance of concatenative programs that is well below what we can achieve with mainstream programming languages?