M4 Pro vs M4 Max

Photoshop has historically not made the most of GPU and multi-core CPU performance. Adobe has been improving this in recent versions, but how well different areas of Photoshop are optimized for GPU and multi-core CPU is uneven. For the CPU, the M4 Pro and Max have roughly the same single-core CPU performance, and the same number of CPU cores, so the CPU is not where any major difference will be. For the GPU, the extra GPU cores on the Max will help the gradually increasing number of Photoshop features that are GPU-accelerated, including AI features.

It’s also a mix in Lightroom Classic:

• More memory probably stops helping at around 32GB in most cases. 48GB might help with high megapixel images (roughly over 35 to 40 megapixels). 
• The M4 Pro and Max have the same 14 CPU cores, so performance of multi-core tasks such as bulk preview generation will be about the same. 
• More GPU cores will give the M4 Max an advantage in performance of GPU-accelerated features, which at this time are mostly the Develop module, Export, and AI Denoise. If you use AI Denoise in bulk, it might matter that the M4 Max should be significantly faster because AI Denoise speed correlates closely to the number of CPU cores. 

On YouTube, the ArtIsRight channel runs benchmark tests that include Lightroom Classic, Lightroom, and Photoshop. In the video you see how those models rank on his charts that include other Macs. Below is his test results video that includes the M4 Pro and M4 Max. Lightroom Classic starts at 8:37, and Photoshop starts at 16:47.

The Max has quite a bit more performance than the pro but the extra memory might be good in the Pro. I would guess the Max 32 core would be more performant in general for the use case here even with the slightly smaller memory if these are the two choices. In my experience, there is only limited gain in performance for Lightroom/Photoshop with typical image sizes above 32 GB of memory with Apple Silicon machines.

I recommend that you have a look at the upcoming comparative reviews on below linked site. Histororically, the reviews published on the site have a good focus on Lightroom Classic and desktop.

BTW, if using LrC and Photoshop together, then best you go for 64GB of memory

I also suggest that when you do make your purchase, don't use Apple's migration assistant and avoid third party utilities such as Clean my Mac, etc.

https://www.youtube.com/c/ArtIsRight/videos