I often need to generate large KML files 10-100MB size.
For example, 5000 features can be handled nicely. Depending on type of feature and how much text/extendedData per feature you might be able to get Google Earth to handle up to 25,000 features or more. I've created a
KML generator that can generate up to 25K features for testing. I tried some tests with 100K places and another with 500K places both of which had issues.
If you generate or split your KML into many smaller KML files such as in 5,000 placemark chunks you can have a parent KML with networklinks to the smaller files. You can have 100's of the smaller files. 4 is definitely not the limit but you may need to set <visibility>0</visibility> on the networklinks to NOT auto-load all the network Linked KML files at once.
--jason