Use existing video card or not

FWIW, I recently built a similar system using only the case from the old. I incorporated a non-overclocked version of the i7-3770 with an Asus 77H series mb, 16GB RAM, an SSD for W7 Ultimate and applications (CS6 and LR4), etc.

The advice I was given with respect to the old GTX 260 graphics card was to try using the system without it (utilizing the HDMI port on the mb and monitor) and see if it was acceptable. If not then to invest in a GTX560 (about 120 USD). The consensus was that LR4 would not use any of the cards resources, and that CS6 might, but minimal.

Again, FWIW.