Have Task Manager open showing your RAM levels during this period and see if that is topping out. I had this problem of lag and stutter and it turned out the CPU etc was running with loads of spare head room but it was my 4GB of RAM that was hitting it max and causing the bottle neck.
I spent £50 upgrading to 12GB and it fixed the issue and now I have no trouble at all.
It is worth looking at what programs are also running in the background that load themselves up at start up and Chrome uses a lot of resources if you have a few tabs open.
So before spending a lot of money this is worth checking as you may be able to fix the issue for little money, you will need to check that your motherboard can take more ram.