I'm getting transfer rates ranging from a low of 25 bytes (yes bytes) per second to very brief bursts of 8 K/s. Average rate is around 550 bytes/s to around 1K/s.
End of quote
One thing to note is that the speeds the SDC reports aren't entirely accurate: the SDC appears to report the total data transferred/total time taken. That is to say, it doesn't take into account time lost preparing for the transfer of each file, or the time it takes for the initiating SYNC ACK message for those files to arrive. Most programs that report transfer speed don't count those actions as part of the transfer time.
(One of the indicators, incidentally, is contained in your message: a sustained transfer rate of 25 bps isn't possible: the lower limit is 256 bytes minus the packet header, or about 248 bytes per second. Only an average transfer rate can reach that low of a number.)
~SDC~