M4 Pro (24GB) vs M5 (16GB) for Photoshop / retouching + generative AI — which would you buy?

I would recommend to get a MacBook Pro M4 Pro, at least 24 or 48 GB, you would find very decent discount now within 2000 for 48 GB. 

My MacBook Pro has been doing great at 32GB, but when you say “Files usually range 200MB-800MG” (I assume you meant MB), then it’s likely 32GB is a minimum for that kind of work, with 48GB being nice if you can afford it. Not sure if you would need more than 64GB, though.

1. Does the extra GPU cores in the M4 Pro or the extra unified memory give bigger real-world gains for Photoshop/AI tasks?

By @Japan Suite

They can, but as always, “it depends.” If you watch macOS Activity Monitor or another system monitor app, you will see the GPU used heavily for some AI tasks. This is even more true if you use the AI features (not just generative AI) in Adobe Camera Raw or Lightroom; you can easily see the GPU max out when using several of their AI features. Even though some AI processing is sent up to Adobe servers, a fair amount is done using compact local AI models that are part of the application installation.

The picture below shows the GPU History graph in macOS Activity Monitor; see that GPU usage spike at the end? That was when I selected the Object Selection tool in Photoshop and the AI started to identify objects in the scene.

The thing about Unified Memory is that it has to account not only for system and application memory needs, but also for all the memory the GPU will need when it’s heavily used. For example, older versions of Photoshop ran OK on your 13" Intel MacBook Pro, but because the Intel 13" only has Intel integrated graphics, it’s limited to 1.5GB of graphics memory taken from system memory and that’s not enough for some newer features. In Apple Silicon Macs there is no such limit, so if for example you have a 48GB MacBook Pro and some GPU feature needs 30GB of graphics memory (that's an extreme example by the way, almost nothing needs that much), the Mac could hand over that 30GB if available. This memory flexibility is very useful for the increasing number of GPU-accelerated features that are raising Photoshop system requirements for graphics memory. 

Where that can be a problem is if a Mac has only 16GB of Unified Memory. If the total amount of system memory that macOS and Photoshop need is already close to 16GB (very likely for the file sizes you mentioned), then it’s possible that the GPU can’t get the amount it would like for optimum performance. This is why 24GB and up is a better idea for apps that need the GPU, and again I personally prefer 32GB and up. 

First of all, generative AI is remotely processed on Adobe's servers and does not use machine resources at all. But there are plenty of new advanced functions that are based on machine learning and AI, and most of these are processed in the GPU, not the CPU. What is particularly important to be aware of here, is that the GPU can use huge amounts of memory processing this.

In Apple silicon, the GPU uses shared system memory, and that means all of that GPU processing will eat up a significant chunk of your system RAM. In other words, you should double the amount you would "normally" need. I'd say 32 is absolute bare minimum, 48 a bit safer, 64 comfortable.

The M4 Pro will be more capable, although you'll really want more RAM. 16GB is marginal for an existing machine and a waste for anything you want to keep. I'd say minimum of 32GB and 48GB is a better investment.