You don't necessarily need to run low presets, try just turning down AA/AF and maybe dynamic lighting.
Is your lag connection related? Lag is a term to describe a slow internet connection.
Can you confirm you cpu is running full speed under load?
My lag is not connection related.
When i ran the game on stock speeds I had 10-20 fps on low presets. I overclocked the core to 800ghz and the memory to 1600ghz and then I could play low on 60 fps constantly. My GPU is pretty much maxed when i check it with afterburner.
According to this chart, your card (the 1gb model) should get 47fps at 1680x1050 on high quality. You have less Vram so yours should be at around at least 40fps. 60fps on low settings sounds about right.