Slowness in your environment can be validated by examing your BES MAGT log. See if there are "No Response" threads, chances are something in your environment is slow.
Sample
{
MAGT log:
[20315] (03/04 12:08:09):{0x1A2} Thread: *** No Response *** Thread Id=0x36, Handle=0x3E0, WaitCount=1, Last Activity: New Message for user CN=User Name/O=Company.
}
RIM Reference:
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