Old hardware
In terms of efficiency I can indeed vouch for P4s being power vampires.
Its interesting to note that although SSDs are very fast they do use a lot of power especially older ones where all the chips are powered at once to make all the memory available without latency.
The chipset is also a known power hog and in some cases uses almost as much energy as the entire Flash array on small SSDs (<128GB) as the regulators are in this part.
I did a few experiments comparing heat production versus efficiency and even a laptop from 5 years ago runs a lot hotter and has a lower IOPS/W rating.
The point at which replacing hardware becomes viable depends on cost, if a business can afford to do so selling their now-obsolete servers to other smaller companies for a pittance makes good sense as it helps them grow into large companies eventually.
A few years back someone got rid of their server because it was stuck in Socket Hell (aka upgrade limit), they'd maxed it out with Xeons + 32GB RAM and it still wasn't fast enough running VMs.