I'm not really that keen on going by the number of postings. There are enough people who have a lot of posts, virtually all questions, sometimes about pretty basic stuff. Similarly, there are many who have only a few posts to their name, but almost all of them are answers, sometimes at a very high level.

My alternative (if technically feasible) would be to have a dedicated sub-forum for reviews whereBoth approaches can potentially be used to create an editing step, to weed out marketing stuff or gross inaccuracies. My personal favorite would be 'c', since it allows users to change their reviews should they or a mod see any problems with it (spelling/grammar/accuracy/...).

But if the majority decides that it's best to separate by the number of posts, I'd say no lower than 500, and no higher than 750, as I think most non-regulars fall out far below that anyway, and it's a pretty good number to see how technically oriented someone really is.