While the game requires a decent GPU to run max, a CPU is still quite important. A GeForce 9800GTX/GTX+ and Intel E7400 can run the game maxed (4K shadow) at 60FR with drops to 55, however a GTX 260 with an AMD X2 4850e maxed (4K shadow) will have larger FR hits due to the lower-end CPU.
Just saying, don't get a very powerful GPU and leave the CPU in the low-end of the range.

As for the Self-Shadowing thing, Self-shadowing takes a very big hit on the GPU's VRAM, Skuzzy said
4096 = 128MB of video RAM being dedicated to one texture. Even with 512MB of dedicated video RAM, you could run the video card out of RAM with this setting.
8192 = 512MB of video RAM being dedicated to one texture. A video card would have to have 1GB of dedicated video RAM to run this setting, and even then it will get close to running out of video RAM.