> Very fast (faster than naive assembler)

Depends on how naive the assembler programmer is, and, I would think rarely, if ever, on modern hardware because the many subroutine calls kill branch prediction benefits. Also, on lots of old 8-bit hardware, defaulting to 16-bit integers will kill performance relative to native assembly in cases where 8-bit integers suffice.

(Of course, you can fairly easily replace hot loops by assembly or (more difficult) change the forth compiler to compile parts to native code, fuse words, etc)