Poor performance - MD3000i as a file server

Greetings folks

I have an MD3000i acting as storage for a PE2950; below is my observation:
PE2950 file copy local drive to MD - ok throughput, up to 70% of GbE, about roughly the same when file copy is from MD to local drive
Client on the public LAN file copy from share on PE2950 (local drive), ok throughput also

However, when the client maps to the file share, and the share happens to be from the MD - I obviously see roughly equal utilisation on both the public LAN and iSCSI LAN NICS (both using the server onboard NICs); but performance is very bad like 7% of GbE.

First thing that came to mind was that the PE2950 couldn't drive both NICS at the same time, seeing that testing from client > server local disk or server local disk > MD worked ok; but the PE2950 is not ancient hardware either (4GB RAM, 2.x GHz), so it can't be that bad?

Thought it might be due to interrupt sharing, but it's been ages since I had to tweak that on a server, but anyway I've tried tweaking those but it does not seem to help.

Does anyone have any leads on where to go to? Firmware is latest on the MD3000i. (15 x 600GB 15K SAS), also updated the SAS disk firmware.

Thanks!