Video card for photo and video editing

Ok my cousins husband is looking to get a computer for video editing and photoshop. He was planning on getting a Mac desktop but I steered him away from that because I told him I could build a better computer for cheaper. What video card should I pair with this. Thing is I've done a million gaming builds but never any for heavy CPU work so really I don't know how much the video card plays in video editing and photoshop. Lets just say at this point budget doesn't matter.

Well obviously you don't want to cheap out I mean like anything balence is important. BUT also like I said I really don't know much about video and photo editing. As mentioned the majority of builds I have done have been for everyday use and gaming. What I am trying to say I guess is I don't know if I need something like a Radeon 7970/GTX 680 or if something lower end will do such as a 7850. Again I don't know how much of a demand these types of programs put on the video card as I don't do any of the things listed above.
Well for direct computing I know AMD is stronger but with things like Photo Editing photoshop NVIDIA plays nicer on the PC because of CUDA. I have heard gripes though on the Editing side. I mean without going into super serious 3D rendering and editing I would think either would be fine. I think its more feeling out what there needs are how fast they want something done.