Zoom vs sensor size -- break even point?
I think I understand the physics of cameras well enough to say that putting a large sensor in a small camera effectively limits the optical zoom that can effectively use the area on the sensor. At least this is practically true with the cameras on the market: the compact cameras with larger sensors have smaller optical zooms.
I also think I understand that digitally zooming is not really different than cropping an image. The subject in the frame appears larger, but only because less of the sensor is being used to create the image.
My question is about the break even point between an optical zoom with a small sensor and a digital zoom with a large one. As a math question, at what digital zoom is the effective area of a large sensor equal in size to a small sensor? Or as a practical question, at what point does an optical zoom on say a Panasonic Lumix DMC-ZS40 or a Canon PowerShot SX700 HS produce a better image than a digital zoom on a Canon PowerShot S120 or a Sony Cyber-shot DSC-RX100 III?