Both of the published articles were very long. One had to be submitted in three installments because K5 has a 64kb limit on article submission text, and the other was carefully edited to fall just within that limit.
I think this was more effective than just asking for feedback in K5's edit queue because I could ask for comments earlier on, and keep updating the copy on my site over some period of time. I think K5 has some kind of limit on the time an article can be in edit.
Of course this means that you have to be willing to publish your rough draft openly, which you might not want to do. But it has the advantage that it attracts more people to give comments.
Here's one such diary entry. You'll see I got some very helpful advice.
-- All my online writing is here.