I've used nothing but synthetics for well over 10 years now without a problem and my engine has a flat tappet cam in it. I can tell the difference in just the way the engine idles from synthetic to dino oil of the same viscosity. I use dino oil to clean up my engine after sitting for extended periods like a year or more and then change to synthetic. It's an instant 200 rpm increase.

From what I've heard and read on the interweb synthetic clings better than dino oil.