I think 2-3, maybe even 4 posts are reasonable.
It all comes down to quality, value, and rewards though.
If someone is posting 5 times a day fantastic content and is only getting $5 a post. It isn't going to make a big difference to the shared reward pool. Now 10 $400 posts a day is another story and is the entire point of the issue.
I work hard on my one a day post. I even have a college graduate(wife) editor. Cranking out 4 quality posts a day would be a full time job. So at the absolute max I would say 4 should be the cap.