i dont think it would be worth the upgrade.... it just costs too much and the perf increase is too small to justify the price. if you find another NVIDIA GTX 560 to use in sli , yes, that would get you some reasonable gains for the cost.
my personal opinion would be to search for such a gpu and if you find one reasonably prices get one, if not bear with the lower settings till you upgrade on the next gen cpu/mobo/gpu-s. right now, you have a mid range build, but upgrading to a higher end simply means canning all your current cpu, gpu and mobo. they still have life in them for about 1-2 years.