Hi @lnfregos,
Welcome back!
This is interesting that you need to delete 60,000+ all at once! It sounds like one of the challenges to learn about when working on an implementation. Feel free to explain the situation more for the benefit of the community if you like please.
As for your question, if you have access to the database using pgadmin might be the fastest way; however, if you must use the API then bulk delete is possible using SYNC import strategy.
From a similar topic, I found a suggestion by @vgarciabnz:
You’ll have all UIDs with the parameter “deleted”: true for each UID all in one request.
Hope this helps!