I got an Asus GT240 512mb ddr5 graphics card which I also overclocked some 10%. It runs Skyrim alright on medium/high settings. And am playing the game now for some 90 hours total.
But next to that in the PC is a quadcore 2500k processor which is currently overclocked to 4000mhz. But the game by far doesn't use all of its 16000mhz total.
Is there a way to configure Skyrim that like one core of 4000mhz is helping the graphics getting faster? Like for physics/gravity? Maybe in the Nvidia settings?
Don't think of your processors as 4000MHz x 4, it simply isn't true. Even if the game used all four cores at 100% utilization it is not the same as one core at 16,000MHz.
CPU cores and Graphics shader cores are completely different animals, the CPU cannot process graphical rendering subroutines. Also a GPU shader core cannot process Operating System and general use commands. Yes, certain CPU do have GPU based cores inside, but those separate and different they just happen to be inside the same package.
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Your CPU is obviously not in question, however the GPU no matter how to overclock it, will always have 96 shader cores. This limits its performance. Usually nvidia graphics cards (with three digit naming scheme) with the last two digits (60-99) are made for gaming. They have more shader cores, more memory bandwidth, and more memory.
If you meet the power requirements getting one of those gaming grade graphics cards should allow you to play Skyrim and other games at much higher settings. If you can afford it I recommend upgrading the graphics card to a 5xx or 6xx series Geforce (note the last two digits) or an AMD Radeon equivalent. AMD uses a four digits scheme, with the last three digits indicating performance (600-799 for mid range, 800-999 for enthusiast).