Lag in Supreme Commander

[Eyesee]

When i play Supreme Commander online ! we were 4 VS 4 when the game begin there was seriously lag as the size of our armies increase . I tried doing many thing like put all the graphic settings down to minimum.

my configuration
Power: 650 w mpt6500 advance
Processor: intel pentium 4 ghz 640@3.35
Graphics Card: club 3d radeon hd 3870 overclocked (ati catalyst maffiche frequencies: gpu 300 mhz memory 1170 mhz. Is that good or is it under powered, it works more pciex16 2.0 in its performance should therefore be increased, the port PCIe frequency is 100 MHz that is normal?)
Ram: Corsair XMS ddr2 pc 6400 (that run only a 400 mhz, cpu limit I suppose)
Motherboard: ASRock p43d1600twins

I dont know whats the problem may be it is my Processor. any suggestions would be appreciated.

[Hitman22]

The problem occur in online or it happens in single player as well .

If it occur in online then it must be your internet connection problem and if it is offline then it could be due to your processor.Supreme Commander really recommends a dual-core processor .