We have a pair of redundant 515e firewalls. A couple months ago users started complaining of slow performace between network segments. The common denominator seems to be segments seperated by the PIX's. We also discovered if we try to FTP files from the inside interface to anything on the outside interface (dmz or on the Internet), the speed drops to about 12 KB/s. No matter what we FTP to on the outside, we never get above 12 or 13 KB/s. I noticed similar performance when we try to do a Windows file copy from a workstation on the inside interface to a Windows box on the outside interface.
I read a few posts on various forums, and subsequently changed the ports from auto to 100/full on the PIX's and the switch. That did not help.
I upgraded the firewalls to 7.2.1 in January, but can't remember from what. It was 6.something, but I don't remember exactly what. Complaints started coming in around March, so it might be unrelated. I upgraded the PIX to 7.2.2 this weekend, but that did not change the behavior.