If you install via SDC then clearly you uninstall via SDC too.
Standalone versions of WB install via an installer & uninstall via Add/Remove Programs.
Your report is the only report of anything like this which makes it somewhat difficult for us to even attempt to debug. Nobody I know has an Acer laptop like yours and obviously Stardock are not about to go and purchase one.
We have ruled it out being a problem with Turion cpus in general and if you have just done a clean reinstall of the OS without installing anything else but WB before testing again then we have ruled out additional apps on your PC UNLESS the clean OS was a factory reinstall in which case it might come with a lot of junk.
If it works with WB 4.6 and not 5.0 then the biggest change in WB 5 was per pixel skin support, but you have said this happens with or without per pixel skins. I ought to ask if the non per pixel skins had per pixel taskbars or start buttons as that could have an impact.
The other thing to do is to put WB into inclusion only mode (and add explorer to the list). This would stop WB skinning anything other than explorer. This would eliminate the possibility of WB upsetting some other app on the PC which is making it stop slowing down.
Another thought is WB5 fades the default button in & out. I assume when testing you do not have a default button visible thats fading in & out.
Finally the only other thing I can think of is WB has a multimedia timer but that uses almost 0 cpu and only runs every 10 seconds. However it does have a requested accuracy of 1ms so I will see if we can reduce the requested accuracy and see if that helps you or not. It should have no impact, but it is something WB4 did not have.