You can try an Apple Script: I am using a script to create two albums - one album with photos smaller than a given pixel size for the longest edge, and one album with photos larger than the given pixel size.
See: Script: Search for Photos by the Dimensions in Pixel Size
And this script will search for the photos and videos by the file size:
: Script: How to find videos and photos in your Photos Library larger or smaller than a given file size
Alternately, give the free trial version of PowerPhotos a try. PowerPhotos can show your photos library in a list view, with column with selected image attributes, and you can sort the photos by the columns. SO you can sort by the file size, with the largest photos at the top of the list.
Power Photos is just my tool to find quickly back to the versions in Photos. I display the photos in list view in Power Photos, then sort them by size to find large "fullsizeoutput ...." files, then ctrl-click one of these photos and select "Show in Photos". This way I will know, which photo is Photos corresponds to the large file. It does not help to search for "fullsizeoutput..." in Photos.
