New MacBook or new AI rig

I have 4000€ budget to buy a new computer for semi pro hobby. But I can't choose.

My main goal is to learn 1). A bit of low level GPU programming 2) how to distribute AI inference over at least 2 GPU.

What I already own: - MacBook pro 15" 2015 16 GB / 256 GB - ipad pro 1 TB - Turing pi 2 & 4*32 GB commute modules

The buying options I see: - MacBook pro 16" M4 pro 48Gb / 2 TB 4049€ -- pros: happy to own a beautiful and portable hardware, can learn GPU programming With MLX - pc rig with 2 3090 128 GB /2tb second hand 3200€ -- pris: can learn cuda, and distribute workload over the two GPU

I don't know which one is better for my goals. Are there better alternatives? Should I consider buy 2 Mac mini? Wait for the mac studio M4?

I already used colab but I am fed up to redownload the models at every session.