Hi tmacka88,
I just did a quick "dd" test on my box & here's what I got:
filer# dd if=/dev/zero of=testfile bs=8192k count=1000
1000+0 records in
1000+0 records out
8388608000 bytes transferred in 14.092086 secs (595270856 bytes/sec)
According to Google that works out to about 567.694527 MB/sec
That's writing straight to the disks internal to the box, which is way more than enough performance to max out a gig-e connection. I can usually come pretty close to maxing out the connection over CIFS.
Personally I think just about any modern CPU should be sufficient for a single gig-e connection....take a look at some of the threads from folks running Intel Atoms or AMD Hudson (E-350) boards and they are evengetting great results. If you give your system enough RAM, use a quality (Intel) NIC's and connect everything through a good stand-alone gig-e switch (don't use the ports on your DSL router\cable modem) and you should be happy.
-Will