While I ran a Beowulf Hyper-V cluster on these (in production) I wouldn't call them 'quite' powerful for today's needs.
I had a stint with PhotoPrism recently and it was faster to upload gigabytes of photos to my Xeon E5-26xx server and run PhotoPrism there (including transfer time) than wait for it to complete the face recognition on my desktop with the Ivy Bridge CPU.
But for a bare packet pusher ie file server, PiHole and the like I would agree it would be more than just fine.
I've got a bunch of these around, either multi-booting diskless (Devuan/Debian/Windows), more than enough for browsing, video calls and light development. Spec is E8400's at 3GHz/4Gb RAM, 1G ethernet, display port and decent sound ('lspci' shows wall-to-wall Intel parts). In USFF ('USDT') format they're great little systems for the price (on ebay they go for less than the cost of the Windows licence they come with, and if they're from a pro-recycler the licence often isn't even locked to the hardware).
Edit: Oh, and being HP they are pretty much clip together, no screwdrivers needed.
Also, if you are generally friendly to the IT person, you may get a few of these for free when they discard these to upgrade. That's how I got mine, anyway.
These machines are very low power consumption (Can idle in the 5W area) and are built to last. I would not hesitate to buy 2 for a redundant server setup.
I have a 8300 at home and recently spent half a day searching for an old driver that would enable WOL, since it's not supported by Windows 10 drivers. I managed to find a compatiable one that wouldn't be rejected by Windows eventually, but it was pure luck. It's a shame libreboot doesn't support WOL.
Please note, that to boot Windows you require a vBIOS to be present, something that is off by default in libreboot, as it's a proprietary blob. It will only boot into safe mode. But you can configure it in the coreboot config menu, though that would go against the libre principle. But the ultimate principle is consumer choise of course.
Actually that's a good question. Perhaps an answer is that they are looking for still-supported firmware or needed WOL as such a core feature and perhaps apps couldn't just run on just Linux, but it is still a good question: why run a closed-source (some might call spyware) operating system on top of libreboot, the opposite.
Although it is indeed a weird mix of going all the way of using a FOSS firmware with the goal to remove all non-FOSS proprietary software blobs on the boot-path and then include them anyways via Windows, but that is of course up to the consumer. The right to use your device anyway you wish, the ultimate expression of libre.
These seem to be fairly available at quite cheap, i think one of these + a nvme adapter and a couple of drives could make for quite a powerful cheap nas
I'd be curious about how the power draw would compare to my current ryzen 3700x which is vastly overkill for my needs, but obviously much newer.
if we can get AMT functionality like remote rebooting in to PXE, then I would migrate immediately for the home lab. For now, AMT is too convenient in combination with Canonical MAAS which does the whole lifecycle when you use these machines as a server.
They are still quite powerful considering they are about 12 years old (Sandy Bridge era).
Hopefully they add 8300s as well.
HP really makes/used make machines pleasant to upgrade and service around that time.