Next Steps

I ran just two miles at lunch yesterday. I normally have an hour for lunch, but there was meeting that took up half an hour and I had to change and get out to the track so I was left with about 17 minutes. It was sunny and the temperature was about 60. (Today it is supposed to reach 70) Something I've observed about my new stride is that when I'm running right it feels like my feet aren't even hitting the ground. It almost feels like they're rolling. My concern though is that later during the day I feel little twinges in my knees; I wonder if I am stressing areas that weren't being stressed with my old stride. Am I doing some damage or are these just minor adjustments? I've never had knee issues. I may be doing too much too soon running a la minimalist. Yesterday's 17 minutes were at 8 minute per mile pace in the Nike Frees. I am going to try mixing up the running a bit more. Today at lunch I will run the old way in the Asics for about five miles; that will give parts tied to the new way a break. I want to do a true barefoot run here soon; that will be short and slow. I'd like to work in a longer trail run as least partially in the VFFs on the weekend. In the normal scheme of things I would be due for about a 20 miler at this point, but I don't know about making that happen right now. Which shoes do I wear, what terrain do I go on, which stride do I use?