As of this date (Sun May 18 12:18:13 AST 2014) the Noaaport data and file rates are, on average,
data rate r = 1 MB/s = 60 MB/min file rate f = 2500 files/min
s = spoolsize in GB
minutes = s*1000/60 slots = minutes*2500
minutes = slots/2500 s = minutes*60/1000
Therefore, each 1 GB in the spool can hold about (1000/60) = 16.66 minutes of data, which is about 16.66*2500 = 41650 files.
So, the recommendation is to set the spooldb slots parameter to 32768 for each GB of the spool. This in turn implies a retention time of about 13 minutes.