[CentOS] RTL8169S-32 card

Hello, I am building a DRBD cluster with CentOS 4.4. Both nodes have RTL8169S-32 cards, Pheenet branded. I'm getting no more than 185 Mbps with the driver selected at installation (r8169). Downloading Realtek's r1000 climbs to some amazing 200Mbps. I am measuring performance with iperf, host to host, with a cat5e direct cable some 2.5ft long. Maybe disk I/O will be the bottleneck in my use case but anyway I feel performance is well under par with this cards. Is something wrong in my measuring setup? Am I right in expecting more speed? Has anyone had this same experience? Resources to compatible Gbps cards? Thanks!