I have a 2.66 GHz mac pro running OSX and a Sun Ultra 20 Opteron 180 system running FC4 sitting side by side in my office. Both have identical 7200 RPM disk configurations in RAID 5, and both boxes are connected to gigabit ethernet. In transfering files over the network, I can get the Sun to transfer files to a network file server at speeds up to 42 MB/s, while the Mac Pro can only do about 31 MB/s. I've tried switching the cables out, etc., with the same results. Any ideas why the Mac Pro gets such poor performance in comparison?