Don't the parallelizing techniques of a 4x build make using them more difficult than a 1x build with no extra parallelism? Couldn't the 32GB 4090 handle more models in their original configurations?
For LLM inference parallel GPUs is mostly fine (you take some performance hit but llama.cpp doesn't care what cards you use and other stuff handles 4 symmetric GPUs just fine). You get more problems when you're doing anything training related, though.