Rotella T 15-40
Dave,
After the cam has broken in, I think viscosity is more important than ZDDP content. I set my bearing clearances tight, so 10w-40 is more than adequate in the summer and 10w-30 in the winter. I also don't get too crazy trying to restrict oil from the cam with radical scrapers, cam tunnels and top end oil restictors. These mods are worth power but my stuff sees street time. All I use is a windage tray to separate the crank from the oil pan. If I could only find a high ZDDP content oil in 20w-50 (after the cam break in), I would not use it in my builds as it would cause more harm than good. Of course, I would use 20W-50 in an endurance scenario in far Southern climes like the Silver State 100 or Baja 1000.
All that being said, Royal Purple is a great synthetic and has never caused me nor anyone I know any problems whatsoever, as long as the engine is oil tight to start with.
Valvoline and Penzoil are my two mineral based oils of choice. I never had an oil related failure using these two oils, but I'm sure there's a few more good ones out there as well.