For batch exporting, there is a utility python script that will try and reduce memory usage as much as possible by batching the exports and restarting zope in between.
It lives in scripts/export_batched.py if you have the egg checked out. Otherwise copy it from github into your own project:
https://github.com/netsight/collective.jsonify/blob/master/scripts/export_batched.py
For a full list of options run:
export_batched.py -h