Basically, do what many on here have said. Get an oil analysis on the used oil you change from. Then you can make a better, more detailed decision on what to use. I persoannly have run Royal Purple 5w/30 with Z-Max since I got my car with 24000 miles on it. Changed the oil every 7500 miles. Now I am at 221000 mles and still going stron. No abnormal issues on my OA tests either.

 

Amsoil Euro synthetic 5W30 every 5k