After creating a new field on my content type I try to edit it at
/admin/structure/types/manage/<content_type>/fields/<field_name> and hit the php timeout.
After some digging around it appears to be caused by the "Default value" select list that gets it's options from EntityReference_SelectionHandler_Generic::getReferencableEntities().
Each time I land on the page it is trying to populate the select list with 25,000 entities and can't manage it in the allotted 5 minute php timeout window.
Is there anything we can do to solve this massive performance hit, autocomplete, lazy load, any other suggestions?