The default settings will be very close to the original graphics, although you will need to disable certain hacks for effects in certain games. (You can keep all the hacks off if you want to, but that will hurt your performance unnecessarily.) You may also want to enable real XFB if you want to get close as possible to the original graphics (but I can't remember how much of a visual difference you actually will get from this when you're using 1x IR, and it will affect the performance negatively).
OpenGL is usually faster than D3D11 on Nvidia GPUs, so I suggest trying that. There's nothing wrong with trying D3D11 too, though.
OpenGL is usually faster than D3D11 on Nvidia GPUs, so I suggest trying that. There's nothing wrong with trying D3D11 too, though.