Whats the best way to find Actors in a Data Layer or StreamingLevel

Using WorldPartition and DataLayers when i remove a Layer or StreamingLevel i need to save the actors in there. Basically think of them as Sectors or SubLevels.

The problem is im not sure of the best way to identify where they are, ie I cant use GetLevel as it returns the persistent level.

I could just use massive overlaps but feels wasteful.