Launch task manager (CTRL-ALT-DEL, Task Manager), minimize it, and go back to your gaming. After you notice some lagging, maximize task manager and look at the memory usage. If it is spiking, you may need more RAM. This will also show you whether your CPU utilization is spiking.
I'm in the car now (be home tomorrow driving 1000 miles) I have an intel i5 , motherboard I dont know right now :/ But give me a day and I'll be back with you!!!!!
True dat. 16GB is overkill for most gaming. That amount of memory is better utilized by photo/video editing software or CAD software. Memory is not the bottleneck here...