HyperTalk is not all that fast. I've done some things to make HyperBBS run as fast as possible, but there are still some annoying delays. Once it's sending out text, it keeps up easily with the maximum baud rate, but it can take a while for the text output to get started.
Rather than trying to fix the problem directly (which would be difficult and would almost certainly mean making a mess of the internal structure of the BBS), I'm going to press on with the next step(s) in the evolution of the BBS. I expect later releases of HyperCard itself to be much faster. That will (hopefully) render the problem quickly academic.