There's no fixed rule here, you can experiment and try different movie codecs (compression) to see what works best for your machine. We recommend using Photo-Jpeg Quicktime movie compression at 1280 x 720 resolution.
Why Photo-Jpeg? Because it is a very low CPU intensive codec yet retains image quality very well.
We offer a free BatchConverter utility software to make it easier for you to convert a group of videos into MOV format.