27" iMac video card options

After 4 years of working off a MacBook air and an iPad I’m going to get a 27" iMac.
Main reasons for the switch are ergonomics, I don’t need an Air and an iPad, and the 5K screen for working with photographs.

My question is the video card. What functional difference would there be between the 570 4 GB vs. the 580 8 GB? Cost is a factor here.

I won’t be doing tons of batch processing of photos but will be working for stretches of time in Lightroom and Luminar. I doubt I’ll dabble in video at all.

I do occasionally play games but that’s curtailed off drastically in the last few years (Xcom 2 is about the only thing I’m interested in right now).

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Generally the only things that tax a graphics card particularly heavily are 3D games and video rendering. Even the latter can be done on lower end hardware, it just takes longer.

Unless you feel the price difference is affordable, I wouldn’t worry when going for the lower spec card. You’ll probably extend the useable life of the machine if you can afford the higher spec card though.

I do a lot of stuff in Lightroom and my conclusion: Lightroom is a slow piece of junk. The last upgrade changed that somewhat, it isn’t as sluggish as it used to be. What’s interesting: with Mojave, OpenGL will be deprecated. I just checked both Lightroom and Luminar (current versions) and there are still OpenGL calls there. So, I guess Adobe and Skylum are both working on the next release which should be Metal (2) only. So, the performance differences will be in the code. If you look at the 570 and 580 specs, there isn’t that big of a difference. The 580 doesn’t have double the amount of shaders, it’s just ~10%. And then it will depend on how pure Metal2 API calls cale on the memory. Not sure… My guess: not noticeable. What really sucks is that Apple ignores nVidia cards…and here again we are looking into crystal balls: will Metal2 perform as well as CUDA? OpenGL/CL were underwhelming compared to CUDA…Ok, this has nothing to do with Lightroom, just ranting.

Thank you both for the replies. My assumption was there wouldn’t be much of a practical difference for me.

I might camp out of the refurb store for a bit looking for a good deal on a 580, otherwise I’ll probably get the 570 and put any extra money towards ram.

That’s curious about Lightroom and Luminar. They both run slow for me, but I assumed that had more to do with the MacBook Air than the programs.

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