A few months ago someone on one of these two LF reflectors pointed me at the Enhanced USART in the 16F688 and later PIC devices, saying how the baud rate could be set as high as Fosc / 4. So getting 3M Baud with a 12MHz Xtal for compatibility with FTDI chip COM ports at thier highest setting.

Who was it and have you managed to do this?   I finally got round to testing a 16F688 at 3Meg   and am getting some funny results that mean sometimes the PIC's EUSART sends the right data, and sometimes it gets itself tied up in knots, sending one character several times

It is not a programming error either, as the code works perfectly at lower baud rates, by just changing the divider.   The nature of the problem looks and feels like something inherent to the internals of the chip 

Andy  G4JNT