TL DR:
No Prime95 rounding errors with the new components, but some other issues.
Temperatures are about the same.
This Ryzen seems to not boost as high as the older one, but (so far) it is stable (at stock). But also I changed the MB.
CineBench R20 CPU multi thread score slightly lower. Single CPU score about the same.
Blender Benchmark times about the same.
Also my Windows 10 Pro (Retail/FPP) does not activate after this second hardware change.
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Long version:
I re-assembled the PC, with the new parts (a different Ryzen 5 3600 and MSI X570-A Pro). I used the stock Wraith Stealth cooler, like first time.
This X570-A Pro came with 7C37vH1 BIOS (UEFI) - oldest version available on the manufacturer's web page for this motherboard.
This old BIOS version was missing the setting for IF/memory ratio. You can only input the frequency values directly.
Another issue I found was that enabling the POST beep had no effect (no beep during POST).
First I booted with the previous Windows install (when I had the same components, except a different Ryzen 5 3600 and a MSI B450 Tomahawk MAX - which I returned because I was getting rounding errors in Prime95 Small FFTs, at stock; it probably was the CPU, but I could not completelly exclude the MB).
I left the LAN cable unplugged, to not mess the Windows activation.
Windows 10 detected the hardware changes and I went straight to Prime95. No errors. Because of the high temperatures during Prime95 stress test, I made several somewhat shorter tests (longest was 36 minutes), but with the previous Ryzen I was getting rounding errors right away.
Then I made a few tests with CineBench R20 and with Blender Benchmark. No errors, but lower scores in CineBench R20, especially in the multi-thread benchmark. About the same score in single thread.
I also did a few restarts and shutdowns. A few times the PC would not boot right away and I had to reset or power it down from the power button. These boot issues were reported by other users with MSI boards (especially with B450 boards).
I decided to flash the newest BIOS - 7C37vH4, which has 1.0.0.3ABBA.
This BIOS fixed the POST beep (now I have a beep, after I re-enabled it).
Also the IF/memory frequency ratio setting is present in this one.
There are other differences, too in the BIOS/UEFI menues and settings.
I booted the same old Windows install with this latest BIOS and Windows removed the GeForce drivers at first start, then re-installed them.
I tried a few restarts and shutdowns and all went well, so I decided to do a clean install of Windows.
I plugged the LAN cable back, inserted the USB drive with latest Windows install kit and selected it from the boot menu.
Somehow, it did not boot from the USB drive, but from the old Windows install. The old Windows installation complained something about Outlook, but I did not investigate. I shut the PC down again.
I have a retail version (FPP) of Windows 10 Pro (with an USB drive and a printed product key). This was installed first in 2017 on my old Haswell PC. Installed a second time after the upgrade to Ryzen 5 3600 (with the MSI B450 Tomahawk MAX) and now the third time.
I use a Windows 10 local account, but I have an Outlook e-mail for the MS Store and the old PC was associated with it somehow.
When I made the first hardware change (with the first Ryzen 5 3600 and MSI B450 Tomahawk MAX), I previously removed the old Haswell PC (old device) from my Microsoft account and from the MS Store. The new installation with Tomahawk MAX board activated with the same product key, with no issues.
After returning the Tomahawk MAX board and first Ryzen, I also removed this new device from my Microsoft account and Store, so I expected to work the same with the X570 board.
Going back to what happened during this installation:
I got again to the boot menu and this time it booted from the USB drive.
Towards the end of the installation process on this new MSI X570-A Pro, suddenly the screen changed colors and had a pink hue. After a few steps of the installation process, the colors/hue reverted back to normal.
When the installation finalized, Windows was not activated.
Also Welcome screen briefly had some pink hue.
I tried the activation troubleshooter's various methods, including a phone activation (with an answering machine, since it was Friday night) and all failed.
At one point, it proposed to input my Microsoft account e-mail and password. This screwed the Windows login, by changing it from a local account to a Microsoft account, but did not activate Windows.
Because of the change to a Microsoft account login, I nuked this install and started over. This time I did not had a pink tint during Windows installation. But the pink tint showed up right after first Windows start (in the desktop). At about the time when it automatically installed the GeForce drivers.
I removed the GeForce drivers with DDU (in Safe Mode), disabled Windows automatic install of drivers and then manually installed the drivers (AMD chipset drivers from AMD, LAN driver, on board audio driver and latest GeForce drivers from Nvidia for my GTX 1060 6GB).
Until I finished with the drivers, the pink tint would show up briefly during Welcome screen.
I ran Prime 95 again (Small FFTs and Blend). Longest run 1 hour 30 minutes (this was Blend). No issues.
CineBench R20 multi thread score still slightly lower than with the previous Ryzen + Tomahawk MAX, but higher that with this configuration when I booted into the old install (with drivers for previous components). Single thread score about the same in all 3 cases (old Ryzen, new Ryzen with old install and new Ryzen with new install).
Blender Benchmark scores about the same (if not slightly better).
This Ryzen seems to not boost quite as high as the previous one.
Everything in BIOS is at stock, except A-XMP memory profile (I have XMP DDR4-3200 16-18-18).
I was worried about the X570 chipset fan. On this board the chipset fan is stopped "in low load situations". So far I never seen it start. I manually started it from BIOS Hardware Monitoring (you can set all fans at maximum rpm from there), to see if it works and it does.
I do not have any PCI-E 4.0 device.
So that's about it, for now.
Monday I will try to get in touch with a human operator from Microsoft and hopefully activate my retail copy of Windows 10 Pro.
Edit:
Minor corrections.