Aero is needed to Window Capture with best speeds possible. As dodgepong said, you should NOT use Monitor Capture under Win7 except as an absolute last-resort.
Also, just as an alternative to using the Scene Switcher (if you aren't running an overlay) you can just put the Game Capture on top of the Window Capture on a single scene; when the game exits, the game capture goes transparent and the window capture shows through. Not the right way to do it and utilizes more system resources, but effective if you don't want to deal with screwing around with the auto-scene-switcher plugin (such as if you only occasionally stream LoL).