...first of all.....a 5400 rpm disk is BELOW spec for operating PPro. A minimum TWO 7200 rpm drives are required, and even THAT is a bare minimum. For now, you should replace your drive with a Crucial M550 SSD...just clone your existing drive onto it. Next, increase the system RAM to the maximum allowed....however, Windows 7 64bit Home Premium allows only a maximum of 16GB....hopefully, that is the version that you have. You can also download MSI Afterburner and CAREFULLY apply an overclock to the GPU memory clock.....monitoring the GPU temperature to make sure it stays low...below 67C should be OK.
The RIGHT thing to do would be to "shoot the works" and get a new Haswell E 5960X desktop system like the one Eric is using to provide the new test results !!! It is so new and powerful, it should "future proof" you for at least SIX MONTHS !!!!