Dennis, thanks for a well laid out list of problems. It does help those who feel they can see some or all of your problems. AVG is by far the most popular free anti virus and I doubt that is your issue. I would not remove that one. Spyware Doctor I know nothing about. If you have the original CD or the download stored on your computer you could remove it entirely using the Add/Remove and see if that helps at all. Superantispyware and or Malwarebytes could be alternatives to trying Spybot Search & Destroy. If you use Spybot S&D be sure it is in fact that program and not a sound alike rogue program. Have you ran any cleaners at all? Not registry cleaners but the Disk cleanup in the Accessories/System Tools folder of XP. Try that and a defrag, it will help modestly. Do you have Google or Yahoo toolbars and are they allowed to run in the background? The Google Toolbar has either 3 or 4 entries in your Startup and using your resources. Click Start click Run type msconfig click OK click the Startup tab Now check each of these items and decide if they do in fact need to run. Google each entry before deciding to stop one because if you stop the wrong ones the computer may not start again. If you stop any you need to reboot. During the reboot you will get a dire warning, do not be alarmed, place a check mark not to see it again and continue the booting.

"tired of the habit Windows has of constantly trying to plug me into deals to monetize me" I don't use Windows enough to know for sure what you mean but maybe you mean those "Modern Apps"? Maybe that's why they're willing to give it away for free? The last computer I bought came with Windows 10. The first thing I did was go though the menu, turn off the annoying (to me) live tiles. Then I removed whatever I wasn't interested in that I could. Some by just removing from "Start". Others by uninstalling (right-click and read). The others that offered no easy way of uninstalling, I used PowerShell to remove. (I think CCleaner now offers a way to uninstall them?) " ... I'm intending to replace everything on my new ssd with everything on my old, now Linux machine ... " That should work the same as the first time. Or easier since you've done it before. If you haven't, you may want to create a boot-able version of your cloning software. If Linux is fast on the older spin drive, it will be even faster on the ssd. Especially booting. " ... trouble getting the computer to let me boot from anything except the Windows C drive ... " On my Acer F12 lets me select the boot device. You'll might want to go into BIOS/UEFI and change the boot order though. So you don't have to select it every time. I just not long ago got around to getting a computer with UEFI instead of the older BIOS. I had a lot of trouble learning how to deal with it. I'm still not 100% confident using it. So... I keep images just in case. And just in case I somehow mess up grub so badly it won't boot (I have): Super Grub2 Disk Of course, if you blow away Windows, you won't have to worry about boot order. I keep Windows as dual boot in case I want to use it. And I do use it, if for no other reason than to boot into and use Macrium Reflect to image my Linux drive. Gives me nice small images and it's quick.

My daughter uses Avast and is satisfied with it. I have used purchased copies of Norton over the past several years and that worked well for me. I have an older XP computer that still works well and I kept it when I upgraded to Win 10, but it is no longer supported by Microsoft, however, Norton will install in it, but Norton will not guarantee complete protection since Microsoft has dropped support. (Microsoft no longer writes fixes should someone finds a way in past present virus checkers.)

I'm not a Windows user so this might not mean anything to you... Since I had never heard of PCmatic, I did a quick search. First, their site's WOT rating, not scientific but... their site is rated 1.5 out of 5. Not good. Yet reading a few reviews leads one to believe their software is the most marvelous thing since butter. Clicking on some of those reviewers, I found their glowing review of this one software to be their only review ever. Which makes me suspicious that their review and probably many of the others are fake. That causes me to lose respect for the company. (that they would use/encourage/buy/whatever fake reviews) (But maybe I just didn't check enough reviewers?) But despite likely fake reviews, it could still be good. Is it? Maybe. I don't know. It seems safe and at least "okay": https://www.pcmag.com/reviews/pc-pitstop-pc-matic As to uninstalling Avast, I don't know but they do offer a special uninstall utility: https://www.avast.com/en-us/uninstall-utility