My PBP manual says:

"The timing of the I2C instructions is set so that standard speed devices
(100kHz) will be accessible at clock speeds up to 8MHz. Fast mode
devices (400kHz) may be used up to 20MHz. If it is desired to access a
standard speed device at above 8MHz, the following DEFINE should be
added to the program: DEFINE I2C_SLOW 1"

My 48Mhz OSC is obviously not "up to 20Mhz".
Do you think it still run at 400kHz by default with a 48Mhz OSC?