A better graphics card, as suggested, would likely help a lot. I don't know if adding more DDR3 System RAM would make much difference; my guess would be little to none.
There may be one, or two things going on such as:
1) Delay in transferring textures from System RAM to Video RAM (going from 1GB to 2GB of VRAM might make a big difference here to allow more permanent buffering of texture data).
2) GPU in the graphics card is too slow. Despite the 65FPS frame rate, game engines are quite complicated. Say for example if you got a better card and managed 130FPS your textures might come in 2x as quick. Probably won't scale like that but might make a difference. I'd still recommend capping at 60FPS (VSYNC ON).
Of course, some problems are simply poor game code which tend to improve with more powerful machines but never fully resolve.