Replistor replication specifications limit

Hi, We have several remote replistor clients replicating to a NAS (EMC Celerra) store using a replistor gateway server setup in the same DC where NAS is located over a 2 MB WAN link from remote to DC.

We have more than 1 such setups. We have been trying to maintain specifications limit per gateway server to be +/- 40. Once that limit is reached I  have checked the performance data for the gateway server and apart from very infrequent processor activity > 25% and  some disk peaking for a small interval there doesn’t appear to be any performance issues with the server, the network card data is almost nil.

That said, if I increase the number of specifications some of the clients already configured starts failing to replicate or the new source client wouldn't replicate. EMC recommends to increase the number of gateway server. Is there a limitation on the OS because hardware performance seems to be absolutely fine? If yes, configuring the gateway server on a virtual environment would help?