Hi!
Can you posting hour system configurations and OS version?
I'm also have a CX-2 based system in my personal lab.
I prefer to test in vSphere environment, but I remember that performance on Windows environment was always over 1Gb ETH connections.
If you show me your detailed configuration then I'll post result after weekend test.
P.S
Mellanox announced end of support CX-2.
Current WinOF release will be a last support CX-2 on Windows!
Check release notes and user guide.