mongodump: are 4 shards with total datasize 575 GB consider a Small Sharded Cluster?
It is not a small sharded cluster.

Mongodump will take around 5 hrs for 600GB and restore would take more than 5 hrs based on the indexes in place on your collection.

My best suggestion is:


If you have a backup already in place taken by Mongo Ops-Manager, use that and restore on the new environment.
If time is not really an issue in your case, use the dump and restore method.
Mongodump and restore method can handle huge databases, if you want to restore few collections then use export and import option.


Note: A small hint i can give here to make the process faster is:

Mongodump will take a backup of the db and collection in 2 files for each, one is bson and other is json. Bson will have the indexes and json will have the data.

So, Mongorestore process will restore the json file first and then start restoring the bson file and apply indexes.

To make this process done faster, first make a mongodump and get all the indexes from all dbs and collections and apply the indexes first manually and then restore the data with mongorestore, this process will save atleast 30-40% of your time.