For personal usage, does it matter though? In most places residential electricity is cheap compared to everything else. In a DC context I feel it matters a lot more compared to the capex.
1x 3090 (350W power limit) already makes it feel like I'm running a fan heater under my desk, 5x would be nuts.
Place and time your use right, and you'll save a bit on heating at winter and/or at nights.
I think the last time any of my computers had a case was back when I realized the pair of 900gx2 cards I was running was turning my computer into an easy bake.
When running inference workloads via something like llama.cpp, only 1 GPU is ever used at a time, so you would have 1 active GPU and 4 idle GPUs. That should make the power usage less insane in practice than you expect.