Future proofing my small monitor (Gaming graphics)

Playing games on my 19 inch monitor, 1400x900, using a HD 4870 1GB

Want to be able to trump current and future games at my native resolution, but with the best image quality and smooth framerates

Looking for a single DX11 card upgrade

Not going to get a larger monitor

With respect to that kind of performance gain over price, whats a good card I should get?
 
Without knowing what cpu you have and what power supply, nobody can make an educated recommendation.

With such a small monitor, I really don't see the point in upgrading the video card at all. Mainstream cards are made for 1920x1080, you wouldn't even be using the cards potential at 1400x900.

You should look at upgrading the monitor first. There is no better gratification than a nice big monitor.