Concur with the PIC at 1 Mhz. If you go with a PIC, try an 18f with has a 4 x PLL and a MSSP module (master I2C) to be exact. Using a 18f4620 MI2C, there is no problem with a PCA9635 (FM+bus at 1 Mhz). Surely the other PICS do to.
Have not tried the 4xPLL to increase the baud rate generator (BRG) of the MI2C over 1 Mhz. Anyone?