Yes, I'm replying to an old thread...but I'll add this information for the benefit of those who may search for this information in the future.
Over the weekend, I put a new PC into service as my primary shack PC. Spotcollector and DXKeeper are running MUCH MUCH better on the new PC.
The software installed/running on the new machine is pretty much the same as the old PC, although the new machine has the advantage of not having any residual "cap" from old+uninstalled or old versions of software.
I now suspect my SC performance issues on the old PC might have been partially addressed if I had done a complete system wipe/reinstall. (The new machine does have a better processor and more RAM than the old machine...but the old machine handled SpotCollector FB when running in safe mode, so I don't think those upgrades provided the relief.)
I will also mention that I did have a change in antivirus/antimalware software when upgrading machines -- I was introduced to "Webroot", which advertises as a low-impact tool that gets very high marks by reviewers who consider the differences in how it operates. On the old machine I had just used Windows Defender. So far (knock wood), Webroot hasn't squawked about or noticeably interfered with amateur radio apps.