Tommy: I never got a definitive answer. My circuits never worked properly and I can't say if it was due to the buffer not clearing or some other bug so in the end I switched to the UART module instead. I prefer SPI for it's use of a clock line but UART won due to it's asynchronous nature which simplified a lot of the code. It's a shame the asynchronous version of SPI doesn't work in my chips.

George: I always use MPASM for PIC10/12/16/18 and ASM30 for PIC24. This question was about the PIC itself though so the language doesn't really matter (and, as Robert said, is why it's posted in Off Topic)