I was just wondering if you had updated your system to the latest build and if so did you find it slower ? I just wondering if trying to go back to 1903 would provide a more responsive system. I could also try changing over to a SSD.
I have upgraded all of my 2007 minis with Windows 10 to the latest current versions. I do not find the updated latest versions to slow them down at all. I would not bother trying to downgrade, as even if you do, Microsoft will eventually force an upgrade (which I find to be a very disturbing policy, but I digress). As most of my posts above refer to version 1903, I should add as a current update that there is nothing special about version 1903 EXCEPT that it is the version that will BSOD if you don't disable or remove the machaldriver.sys file. As the current best-practice, I will add "Either install the latest Win 10 build to start with, or update to the latest build if you install an earlier version."
For your speed issues, I'd say the two obvious things you can do are:
-Upgrade the CPU to the T7600, and
-Switch to an SSD instead of a mechanical hard drive.
I think those two both make a noticeable difference. As to whether the machine feels slow, I think it depends a lot on what you choose to do with it. I've tried streaming live television from my cable company and it's just problematic and slow. I can do it, but only in a small window, the fan spins up, and occasionally the video skips or drops out. HULU and Amazon Prime video are a little better, but only in medium to small windows. The video chipset in the Mac Mini 2006 and 2007 models is a serious bottleneck, and there's no way to upgrade it. You're basically resigned to using these computers for other things.
Things I'm doing with mine:
I have Office Professional Plus 2019 running no problem, for MS Word, Excel, PowerPoint, and OneNote.
I have Adobe Creative Suite 3 (quite old at this time, but still very useable) working just fine for Photoshop, Illustrator, Acrobat, and InDesign. I believe CS5 and CS6 will also install and run without problems as well.
I have Appleworks for Windows (also quite old and obsolete, but I loved Appleworks) running on it no problem.
Obviously, the latest version of Chrome works fine, as do BitTorrent clients.
With Chrome I play Youtube videos, music, etc.
I run various versions of SPICE electronic circuit simulation software without problems.
I run XSim speaker response modeling software on it no problem.
Notepad ++ runs fine for XML document writing and editing.
VLC player works fine for playing videos, but full-screen video skips frames, so windowing is necessary.
The system can play music files no problem.
I haven't really tried things that I know it's not going to be good for. I'm not going to edit video with it, although it would probably handle 2-channel audio editing with certain apps. I don't game with it, although old games that aren't video critical will run fine. I installed Sim City 2000 on it to see if it would run, and it ran fine.
It makes a pretty decent basic computer as long as you don't need massive processing power or modern graphics processing. I'm interested in hearing what other people do with them, as Windows 10 can basically give a new lease on life to these old Macs which even Apple abandoned a long time ago. (Let's be fair: Microsoft abandoned them too. This isn't a supported configuration, but it DOES work. You just have to jump through a few hoops to get there, but it's not a hack, it's just a little tricky to install and requires the right resources and helps if you upgrade the hardware.)