Going with the "it depends" answer. How many files are being processed, how often are they processed, how big is each file that is being processed, how long does it take to process each file (average may be good here), what else is occurring on the system, what is the system configuration (processors, memory, disk (SAN or DASD)).

As you can see there are a lot of variables. You may just need to play with the values until you find something that statisfies your SLA for processing files as well as the other requirements of the system.