I have been out of the loop for a long time, but AFAIK gforth-fast is still quite far behind the commercial forths when it comes to speed. I believe there is still room for improvement of forth speed, but iirc the VFX forth people didn't think it was worth the extra compilation time. Back then it compiled a 1MLOC project in 29 seconds, and the resulting code was plenty fast. As a baseline, a fast non-optimizing compiler should be able to compile about 1mloc a second for a moderately simple language.