Aero peek is actually pretty damn useful to tell which program window you’re tabbing into — but the delay is a good few seconds.
I found a SuperUser post that explains how to set this delay.
Set a registry key at:
In that key, create the following DWORD value: LivePreview_ms and set it to the delay (in milliseconds) of the first live preview.
I set mine to 1 (0 doesn’t work) and it’s instant!