Can A New GPU Rejuvenate A 5 Year Old Gaming PC?

Upgrading doubles the overall frame rate. Opting for Very High detail and enabling tessellation and soft shadows cuts the final frame rate somewhat, to 54 fps, but further improves the game's visuals.
In most of the games we tested, the quality difference between DX11 and DX10 wasn't noticeable. Shogun 2 is different. First, here's the GeForce GTX 260 against the GTX 660, both at High detail. This isn't the same frame, but it's as close as we were able to match, as shown by the movement of the leaf.
Look at the trees in the background. Notice how they're slightly blurred and shadowed in DX10 mode? This is one place where just shifting to DX11 makes a significant difference for these NVIDIA powered cards, even if no other detail settings are changed.
Here's a screenshot from the same sequence, at Very High Detail. Again, we matched the frame as closely as possible.
It's a nice argument for upgrading given that you get to keep most of the FPS increase, while also increasing graphics quality and improving the level of immersion possible with the game.