Background software and memory optimizations are most of the time useless, unless your system is completely overwhelmed by workload, and even then you gain only insignificant speedups.
If you don't/can't obtain more performant hardware, your only option is lowering graphical settings, starting by resolution and raw texture detail, passing by advanced effects (SSAO, Post Processing, Motion Blur, Bloom, Depth of Field, Volumetric effects, Dynamic Lighting, hardware specific AA technologies), all the way down to basic ones (extra detail settings, hardware locked solutions like Physx, basic MSAA and Anisotropy Filter, using DX9 libraries where possible).
Also, a couple side notes you (or many) may or may not agree with:
- If you value graphics over anything else in a game, you're never going to be happy; you can only find true realism in real life, unfortunately 😉
- Maxing out every possible detail in a game doesn't ensure you will have fun with it.