As far as I can tell from the specification, the Maxim MAX3100 can lose bytes if the FIFO overflows and the softwarae cannot detect that this has happened. Of course, the software should be quick enough, but real life is full of nasty surprises. The CRC should detect it, but see earlier remark.
I have to hook a PIC16F876 to a Cypress 8051 using the debug ports (so no CTS or RTS wires), and please do not ask why. I do not want to chop the messages up into 8 byte pieces, and have a protocla layer to avoid FIFO overflow. Are there any (better) SPI UARTs around?