I am editing on a PC and want suggestions for upgrading my Graphics card for Lightroom and Photoshop with the possibility of running 4K video as well.

I run a G-Force 660 (Got it for free when my brother built his pc)
AMD 8 core 4g cpu
ssd hard drives

and a 950w power supply

You may want to try the urban commando section. If you can find another one or two you can run two or three way SLI. There are some impressive cards out now but they are probably around a grand
 

Actually, this is GPU salad days at the moment. You can get the 6th best GPU ever made (GTX970) for ~$300.  That's twice as capable as the 660 that you have.

But, do you actually need a new GPU? The 660 supports 4K and image editing isn't especially GPU intensive.

Are you also video editing at high resolution? You would likely see some improvement. Do you also use that PC for gaming? You'll definitely see improvement.


If you can find a second 660 cheap and you have a second suitable PCIe slot then you can use the pair in SLI but you may also need to upgrade your case (for additional airflow) and/or your power supply (you've got enough power with 950w but you may need additional PCIe power connectors).

Note that the 660 does not support 3-way SLI. Also, 3-way SLI places significant thermal and power loads on your system for mediocre improvements (3 and 4-way drivers are not especially optimized).


This will help you if you're shopping around:
http://www.videocardbenchmark.net/high_end_gpus.html