PE2950 with Broadcom 5708c Netxtreme II NIC - performance and network problem

We recently bought three PE2950 servers with 1Gbit Broadcom 5708c Netxtreme II onboard NICs.  Windows 2003 R2 standard SP2 x64 bit edition is running and nothing else.  I didn't notice the network performance problem until we replaced our 10/100 server switch with 1Gbit 3com baseline 2824 SFP plus switch.  We also have six other no name servers with Intel NIC on the same 1gbit switch.   Our entire network is 1Gbit switch network but very few clients have 1gbit NICs. 

 

Prior to replacing 10/100 switch with the 1gbit switch, both the PE and no name servers worked fine.  The network performance issue with PEs started after we put the 3com 1gbit switch.  You can see my stats below.

 

Dell Servers on 1gbit switch: using iperf ( http://sourceforge.net/projects/iperf ) to transfer filename.txt between a PE2950 and windows xp sp2 client 
9.0 sec   304 MBytes   284 Mbits/sec - client with 1 Gbit NIC
27.0 sec   304 MBytes  94.5 Mbits/sec - client with 10/100 Mbit NIC

 

Dell Servers on 1gbit switch: using SMB (UNC path \\server\sharename\filename.txt ) between PE2950 and windows xp sp2:
10 sec   304 MBytes   284 Mbits/sec - client with 1 Gbit NIC
45 min!!  304 MBytes  eventually errors out without tranferring the file. - client with 10/100 Mbit NIC.

 

Tranferring the file between PEs or between no name servers and PEs is fine. 

 

As you can see, the 10/100 clients are having problem tranferring files to PE using SMB.  

These clients don't have any problem with the no name servers/Intel NICs.  I am not teaming NICs on PEs.  I am experiencing the network problem on all three PE 2950s we bought.  So this is not isolated to one server.  Also, I tried swapping cables, replacing different 1gbit switch brands, upgrading the Broadcom drivers, etc without success.  Dell support couldn't explain why the no name servers with Intel's 1gbit NICs work fine on the 1gbit switch.  I will call three 3com on Monday to see if they have any solution, but I think it's the Broadcom NIC causing the problem.  Any help is appreciated.

 

Thanks