Well here's what I've experienced so far. I have 6 pretty large niche site. The one in the biggest niche is the only one I have ranking well (number 6 on a 33,000 exact a month keyword). I did the least backlink building to this one. Here's why I think this one ranks so well. When I first set up my sites they weren't meant for me to SEO so I never put my keywords in the title. Obviously when I started doing SEO I updated them all, but since my now well ranking one had the keyword in it's actual name, it always had the keyword in the title. It was up for 4 - 6 months and with no backlinking it's at spot 6. I'm guessing since no one did on page seo for my other high searched keyword, all I need to do is leave some of my sites for a few months. I'm sure backlinking will speed up the proccess though.