Why don't you add all your data to the hidden window in bytes, then use /filter on the specified column, without repeatedly calling an alias.
If you are worried about getting the sizes back in their original state, like kb, mb, whatever, then simply add an ID to your data. Like for each line, add a flag, that will state what the original file size format was, but add the size in bytes. If you have to deal with those sizes later, you can format them easily by retrieving the value of this ID, and using $bytes to format.
I'm sure that adding such ID won't hog nearly as much resources, than repeatedly calling an alias to sort.
Greets
