In my experience, even 1 producer caused a full database lock for hours on our production server. We have 1 mongo server and an erroneous scheduled task of ours started at about 6am. It's only one process but the task basically re-syncs an entire collection (which was about 80,000 writes).

That single producer caused wide-scale locking/hanging for all readers on the website and I had to manually stop the task during business hours because of that. Oy!