Sure videos a full different ball game though. You look at intel with their quicksync dedicated on the CPU itself. It's much simpler and more standardized than RAW formats that are company specific. GPU only helps if the software can be coded to use it which as I said most RAW programs don't seem to be doing due to the complexity. I think another part is the quality also can suffer using these things so they're good for previewing but don't help with the final rendering or if they do, it's of lower quality than when rendered with the CPU.
Yes, this is correct. GPU doesn't matter for images unless there is code written that talks to it, takes advantage of it, etc. Otherwise it just passes the graphics information through at a fixed rate as it receives if from the OS. Video isn't much different, it's just redrawing images faster but video isn't 3D rendering. Games are written to exploit the graphics card, engine, etc. That's why some graphics cards work better for some games. Even Windows now exploits the GPU a bit to help render the Aero interface. Adobe has begun to try to write some of their code to exploit the GPU on some cards but that's also pretty minimal at this point. I have a nice middle of the road nVidia GeForce 8400 GS Graphics card. Not top of the line but no piece of junk either. Around $200 back when I bought it a couple years ago. Win7 Pro Enterprise x64, i7 CPU, 32GB RAM. SSD for the OS. The preview pictures in Lightroom 4 still drag a bit. Nothing I can do, Adobe did something with LR4 to cause some latency. (It was faster in LR3.) Exporting, photo tools, etc all do pretty well considering there is a lot of CPU being used then.
Bottom Line, if money isn't an issue, get the best video you can but if money is tight, don't bother. Either way, it won't change the performance much if at all for photos.
BTW, I met an IT associate of mine today and eventually, the subject of his MacBook Pro came up. We discussed briefly how much it helped him with some photo and web development things he works on all day but it did cost him $3200 + over another grand for the large display he uses with it. And then there's the software, Parallels and Windows 8 he runs on it. I mentioned this thread and we quickly agreed that the iMacs are essentially a waste of money for doing any serious work like photography, video, graphics design, web dev, etc. Lower end CPUs, graphics, lower memory limits and slow 5400 RPM drives which he reminded me about. Even the display isn't as good as what you could get other ways. In essence, not worth the money compared to other (more expensive but capable) Apple mac alternatives. Sorry folks but you're just not going to get a standout mac photo workstation for under $2000. Adequate maybe but not exceptional. Not new anyway.