[exim] Mail throughput

Hi,

Just thought you all may like to know what sort of mail throughput I am
getting from exim.
At the moment my mail system is hitting a celling at just over 580000
M/hr outgoing which I think is pretty damn good, many thanks to all you
exim devs out there. Incoming is handled by another server so does not
figure in this figure.
FreeBSD 8.2 with 8 cores, 16G ram and a heavily modified exim
configuration.
No names named but this is for a large publishing company so hopefully
all legit mail with unsubscribes and should be all opted in, just in
case anyone was wondering.
What sort of figures are other people are getting?
Guess I'm looking for any configuration hints from anyone who is beating
this figure or perhaps I have hit a natural limit, it certainly looks
that way.

Best regards

David