It was a one-off I built for a water utility in Connecticut. I'm pretty sure it was an embedded XECOM 2,400bps modem, but I don't remember how I figured out it

It was a one-off I built for a water utility in Connecticut. I'm pretty sure it was an embedded XECOM 2,400bps modem, but I don't remember how I figured out it was faster to do that than to use a 56.6k modem which I would have expected to be faster. Since at 28.8k and higher the modems are negotiating more than just frequencies (phase shifts and bit compression are also negotiated, IIRC), telling a 56k to run at 2.4k should have the same effect.