I would recommend Amsoil synthetics as well. They have a wide variety of viscosities to fit your needs and all have high levels of zinc. Personally, I use the 5w20 Dominator. My engines exhibit excellent wear characteristics. Different viscosities will affect the average overall oil pressure.
http://www.amsoil.com/techservicesbu...t%20tappet.pdf
Feel free to PM me for sources and more info.