Nice detective work. You did exactly the right things to find out what was going on. Some things are harder to figure out, this one you lucked out on, that it wasn't settings something in the system that was slowing it down, installed or not. Best is to install things one at a time until you get to the thing that killed you, then don't re-install it again after a clean wipe!

I can tell you than any screen widget has the potential to cause lag. Any time a widget registers, it gets requests from the desktop manager on occasion. Anything from being scrolled onto screen, periodic updates, events, etc. They also have the ability to register all kinds of hooks into the desktop and the system, and generally are the main reason for display lag. If you can terminal in via ssh and it's all running fine, but your display is laggy: It's likely a widget.

Tons. I use QBW (QueenBeeWidget) for about 10 things on my various desktops. There are scripts out there for just about everything. You can set it up to just add a button that runs the kernel-config command to load a profile on press. And if you want something custom, you can make your own pretty easily.

Mind you, you can cause lag with QBW too if you're not careful. Anything that updates periodically can become a problem. Bet to keep it limited to "on desktop view" or "on pressed". With the latter being the safest option.

Here's a clip of a corner of one of my desktops showing the widgets I have setup. The two octagonal ones are for network stuff, the square ones are for speed changes and battery checking. The "SpeedUp" button sets up a 800-1100 profile (very rarely used). The "Stock" button sets up the default 250-600 settings shipped by Nokia. The "900" button sets up my default 500-900 setting, which you can see is green (active). The last one updates on screen refresh with the current battery level.

Lots of options with QBW.