Aero is a strange beast indeed, so allow me to slightly enlighten you on one of MS' biggest fuckups.
Back in the good 'ol days, you had a trouble shooting option for graphics cards, where you would change the acceleration level for your desktop (it was mostly to stop visual corruption of the mouse pointer). It didn't interfere with DirectX due to it having it's hardware layer separate to GDI's layer, however it crippled OpenGL because it used the GDI layer to talk to hardware.
Skip several versions off windows & you hit Vista.
On versions of Vista with Aero, they tied the desktop's acceleration to Aero's options. It was a pretty logical decision TBH (accelerated desktop trouble shooter inside an accelerated desktop), but there's problems.
Turn off Aero and your DirectX games will run faster because Aero uses DirectX to render itself, but OpenGL apps once again suffer because it turns off the acceleration it needs.
To make matters more complicated it's also hardware & driver dependant! A few drivers were written with the good sense to separate GL from the rest, but things like that are soon forgotten in future versions.
If you have slowdown problems with Aero off, and you actually want Aero turned off the best solution is to just uninstall Aero.
History lesson over ;)