I just read Jason Robillard's post on stride length being the 'most important element of good form'. Go read it here. Basically stride length and cadence are about the same thing, and he talks about the 180 SPM and how to find your own personalised perfect cadence. Also if you haven't read anything by Jason, well you're in for a treat. I just love the his badass attitude authentic voice. He's literally one of my favourite people on the web.