The Iron Game engine is processor speed dependent and is a 32bit game that doesn't use over 2gb of ram let alone 4gb of ram without advanced methods and modding.
On the plus side the engine only uses one CPU core but uses it very efficiently.
It won't matter how powerful your graphics card is esp when you increase the graphics level to highest. Therefore the only way to ensure you get a performance gain is to lower the graphics detail or:
Overclock your CPU to allow the processor to send data faster to your graphics card along the ram.
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Advanced approach is to also release resources used by your operating system on the CPU, RAM and GPU.
Download: Tune-Up Utilities 2012
and use the Turbo Mode as it will be clearly described and displayed so you won't have problems.
Try Tune-Up utilities first because it will solve most lag issues.
Windows Vista/ Windows 7: also make sure when you go to your systems control panel go to Power Options and choose the "high performance" power plan.
Good luck