Don't forget that the pre-defined setting you start from before making your tweaks can have a massive impact on performance, since they affect things like the size of character/world textures and so forth. Use the default setting and set it to Low/Medium/Whatever and then turn off the things you don't want, etc. If it's running bad then start again from a lower default setting. The individual tweaks will generally have a smaller impact, other than DoF and the UberSampling. SSAO is also pretty demanding, depending on your graphics card, so play with that too.