I assume that the border is something like 1000, since it is very difficult for the browser to cope with a huge number of instances of the smal object. For example, if you load hundrets of point features from KML, it becomes quite slow in every JS web map infrastructure.
The best way to solve this problem is to use server-side components to filter objects. For example, streamlined stream layers for low zoom levels and just a stream of nessary objects within your current map view using the bbox filter strategy.
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