David have you tried copying your sbin file and greylist-filters.json somewhere else and deleting the ones in Settings? Just curious if you see better behavior with it smaller, maybe only do this for a little while to get an idea how it performs then swap your old greylist + filters in so delivery delays don't get too bad. Restarting SmarterMail in between moving files.
Also I don't doubt at all that Chris see's a lot of spool traffic, there is an impressive amount of I/O going on at any point in time on his machine. A lot of our optimizations and improvements have come from being able to work on environments like that.
@Chris how big is your greylist.sbin?
Matt Petty
Senior Software Developer
SmarterTools Inc.
www.smartertools.com