NSPI setting within EV

Hi

I have a custoemr who understands the need to increase the NSPI setting for EV to work effectively but is a little nervous in setting it to fffffff as suggested in the EV whitepaper.

Is there perhaps a rule of thumb for a lower figure based on the number of EV mailboxes that can be set and monitored for errors? My customer has 3000 mailboxes so I'm lookgin for an NSPI setting suitable for that size of environment.

kind regards