A few days ago I had to convert 113 raw photographs with Bibble; my iMac took 30 minutes to complete the conversion. Today, I had a 116 new photographs that needed converting. This time, the iMac took 1 hour and 33 minutes to convert 116 photographs.
I have no idea why it took so much longer - 3x longer than before. I had no other application running on the Mac at the time.
I haven't rebooted the system in a couple of days; I hope that I don't need to get in the habit of rebooting my system in order to regain system performance. Tomorrow morning, I will reboot the iMac and reconvert the same 116 photographs to see if the slowdown is a result of a "dirty" system.
As of now, I am at a loss as to why the iMac was so much slower doing the raw to jpeg conversion.