Hi Manuel,
Can you tell me more about the types of images you are using? Do they have many layers, or layer comps? What's the bit depth (8, 16, or 32bit)? Do you happen to have any other applications running at the same time as PS? I ask because I've created big files on my 5K iMac and am not seeing the performance issues you describe. I'm still convinced we can find you a solution to mitigate the performance issues you're experiencing.
Thanks,
Adam
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