I understand your sentiment, but if the pc is that important to you, simple answer don't. When you load anything there is no guarantee you won't cause breaks, especially if from outside repo, in which case you are on your own. I am sure you already know that.
Since you ask the question I assume you are not running multiple OS on your system, because if you did you would no doubt have a sacrificial test install?? This could be the way to go, if anything goes wrong you just clean out the partition, assuming it is limited to the test partition.
Personally I have not had it running on KDE 64 but on KDE 32 it runs fine, but then I can afford a physical meltdown and minor crashes I can recover from via backups. This of course can take lots of time, probably this is a significant factor for you.
What is the chance you can obtain a cheap second hand pc and use just for testing? You can just walk away from it at any time if problems and return later when time permits.