You might be surprised: my Amiga 4000T with a 68060 processor, and full complement of cards (graphics, network, sound) has no fans other than the case fan - all running off a very modest (by current standards) power supply: because there's very little heat generated.

And while I'm missing many of my favorite modern apps, for many tasks the productivity is still unequalled: near-instant bootup, hugely responsive, and a beautiful elegant operating system.