Which computer should I buy: Mac or custom-built 5090? [D]

70% of my projects are fine-tuning pretrained models or using them to build custom pipelines; the other 30% are training models from scratch. Most of my projects are image/video-heavy machine learning. Sometimes, LLM is involved. I know that having Mac as an option might be a little counterintuitive for serious model training, but since lots of my projects rely on large pretrained models, VRAM really matters. And, it seems that Apple is trying to catch up to NVIDIA's CUDA with their own MLX, so maybe even training on an M5 Mac machine isn't that bad? Can anyone who has tried training on an M5 MAX with MLX please share your experience? If you were me, what would you choose? (I know a Pro 6000 would meet all of my needs, but I really can't afford it right now...)