8000 Baud (Symbols/second)

According to the spec[1] for the "analog modem" (the one in your office, house, etc)

  6.2 Symbol rate

  The upstream symbol rate shall be 8000 symbol/s derived from the digital network.

1 - https://www.itu.int/rec/T-REC-V.92-200011-I/en

57600 baud is incorrect. It was 57600 bps which was achieved over a 3200 baud connection by utilizing sophisticated signaling and compression.

https://tldp.org/HOWTO/Modem-HOWTO-23.html