I already had 2x 5070's that I had purchased a year or more ago, so getting an additional two to fill up the PCIe slots on the motherboard seemed reasonable.
I did some math/shopping as well. To get 48GB of VRAM you can get 2x 3090s but that is $3k. A single 5090 is $4k but has 32GB, great for running models like Qwen 27B but maybe nothing else depending on your model settings. Already having 2x 5070, where each card is around $600, it made sense for me to get two more which was $1200 and the memory speeds aligned.
The best value option if you're building from scratch is go with 5060 ti (16GB VRAM). Each of those cards are $570/each on Amazon, cheaper than 4x 5070's. Only downside is memory speed is slightly slower, but you wind up with 64GB of VRAM and you can run big models and small models alongside each other comfortably.
In my setup I ran Qwen3.5 9B for fast inference on simple things and Qwen3.6 27B Q6 for coding work. But I ran into stability issues, so I use llama-swap to dynamically swap models. But with 64GB of VRAM, you wouldn't have that issue. There is overhead to loading LLMs into VRAM that isn't clear, so having extra VRAM is a helpful buffer.