Broadcom NetXtreme BCM5788 severe performance problem

Hi

I have an Msi mobo with an integrated Broadcom NetXtreme gigabit ehternet
that has big performance problem
i tried 2.4.x with tg3 and with broadcom driver and 2.6.x with the same
result
a simple ftp transfer cause a 70% cpu usage and 6Mb/s, same hardware with a
cheap 8139too can transfer 10-11 Mb/s without notable cpu usage
this performance with lftp, with konqueror 1-2Mb and 100% cpu usage
lan is 100Mbit full duplex
i tried also to activate tso with ethtool and disactivate napi (with patch
posted on this ml) but without any luck

any hint?

thanks 

        -Ale