Thanks for the reply.
I up the data rate after initialisation to 12MHz, although most of my measurements are done at 6MHz. I found only marginal differences betwen the two. The max SPI speed I can achieve is 12MHz as this is the maximum my uC can run at (half bus speed).
Am I right in thinking that, even with two buffers (one data, one filing system), the FAT table still needs to be read into the file buffer to search for the next free cluster, and that the larger the number of files (or rather the more card space is used) then the longer this search takes? Therefore as far as using the TinyFatFs as opposed to FatFs, there is little speed advantage?
Has anyone out there done any write speed measurements?
I'm going to look at porting FatFs on to my uC over the next few days. Then maybe consider going for a PIC24 as there seems to be more online support for using this chip in this application. It may be that even at 5MIPS my processor just isn't fast enough. What tools are available for this chip - especially if they are free!!