[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!
-- 
Eduardo Grosclaude
Universidad Nacional del Comahue
Neuquen, Argentina