Something to also consider....
Framerate is a combination effort of your entire machine. By this I mean, you have to have a good HD(SSD) feeding info to your CPU(main processor), which then gives info to your Video card that then displays on the screen. The problem of framerate can easily be something OTHER than video card related, especially if you are not seeing any improvement by changing of graphics options. Something to look into is using monitoring programs and or task manager and watching what is going on while you are getting the low framerates.
Things to look at are how much activity you are getting on your CPU, and GPU(video card) and how they compare. If you are pushing your video card and it is lagging behind, then you would expect to see close to 100% usage, same with CPU, or HD. Somewhat recently I helped someone find out that their bios settings were stopping their CPU from running up to full use....they would see that the CPU would only run at 2.4Ghz out of a 4Ghz ability, which meant it wasn't supplying enough data for the video card to run over about 40% use, and thus ran 15-20 FPS.
So you need to see what your machine is actually doing while it is acting up.