looking to do some segment sourcing on Journal Entry lines (Customer record on line --> sources other line segment fields) when Journal Entries are CSV imported.. some imports might have 6000 lines will a UE script be able to handle this kind of import? Or should I handle this using a scheduled map reduce?

A UE will be fine if you build a lookup table at the start so that you don't need to do searches/lookups for each line

thanks very much!