How to identify system speed bottlenecks?

My system is really quite old and I am in the process of trying to find something within my budget, but in the meantime I am also trying to make sure I have things setup correct.

What I mean is it seems my system should be pretty slow, I have 4.1, KDE, and run lots of appvms at the same time, the thing is when i look at the CPU usage I dont see huge spikes or it running high? I have an SSD drive but I would think that would impact say start up of appvms not speed of apps in those appvms or “eye candy” things like the KDE show all windows all of which seem to be pretty slow but I dont see mem or proc spikes when using these things?

So, I wanted to ask if there was something(s) I could run for a few hours that would show me where the bottleneck is? While my “knee jerk reaction” is need-new-hardware but I know older hardware is not always the culprit.

How do you measure CPU usage? The common system tray widgets or commands like top or htop only tell you the CPU usage inside the appVM or dom0. You also need to look at xentop. I’d be cool (but maybe unsafe) to show a grand total in dom0.