The only place I really worry about keyword density is within my <title>, within my <h1>, within my <h2>s, within my link text that I use to interlink pages or for backlinks. As far as the basic content on the page, I try to use the keywords from my <title> but I write copy as if I'm explaining the topic to a friend or relative. I don't worry about density. If it sounds natural but you use the words your <title> is targeting from time to time, you'll be fine.
I'd say the keyword destiny in the algorithm is constantly changing. Keep going for 3-8% and you'll see what I mean. Yes, thats right, keyword destiny. Because it reminds me of McFly in Back To The Future, lol.