I'm currently deciding between the two GPUs as well, and I'm torn, worried that the slower card won't be enough those 3-4 years I need.
Aevan, if you would be so kind to share, how DOES the m290x actually handle Witcher 3? For example on 2560x1440 and 1920x1080?
I also noticed you're an illustrator like me. Do you get any brush lag in PS (I have CS6) in higher res art? Thank you!
I think I can give you an answer that will satisfy you.
First of all, I ran Witcher 3 in 2560x1440p at high settings with only shadows set to low. I didn't try other settings, a friend told me that shadows are super-demanding and I just set it up like that and tried it and it worked with a steady 40+ fps.
I can also tell you that I tried a lot of modern games as well and that they all ran fine. Surprisingly so, in fact. Apple is using a slightly overclocked version of M290X which runs almost identical to Radeon HD 7870. So, this is something you can use for comparison. However, if you're a serious gamer, you might appreciate the M295X as it's even faster (but it does heat way more).
Now to the important question: Photoshop performance.
Well, first of all, you might be surprised to learn that GPU doesn't affect brush lag at all. In fact, you'd probably get the same results with an integrated Intel GPU. Sure, some effects are rendered with the GPU and it's used for displaying the image (smooth zoom, no jagged edges, etc) but the brush, and most of Photoshop heavy lifting is done by the CPU.
There was some history with brush lag on Mac in general, especially with Photoshop CC (the previous one), but it was fixed later. You should have absolutely no issues with CS6, and if by any chance you did have some, you'd have them on M295X as well.
But to answer your question - no, I have no problems on my i5 M290X iMac. In fact, it's really good - and I work with large files (and also use a Wacom Intuos tablet so I'd notice brush lag that one might miss with a mouse). It is perfect for illustration and I expect it to stay that way for years to come.
A better example for the GPU usage is, actually, Lightroom 6. It uses the GPU for most computations in the Develop module and I can tell you that it's REALLY fast. In fact, any app that uses the GPU runs a lot better than those that rely mostly on CPU. If there is a bottleneck, it's never the GPU (not counting the issues with Mission Control, which is Apple's fault).
I recommend the M295X only for gaming, really. There is no difference in Photoshop performance between M290X and M295X (there is between i5 and i7 - not much, though).
I hope this helps.
