what oil to use

i have heard even from engine builders that only the first few thousand miles require the higher levels of zddp to aid in cam breakin. after that, you can use whatever oil you want, since you should change it when dirty regardless of mileage. i have also heard that synthetics of the same weight are thinner and aren't good for older engines because of clearances aren't as tight as freshly rebuilt older engines or newer engines that have ohc's and tighter clearances.