What is a good number to shoot for as far as zinc content? I see Valvoline 10w30 is 760 for zinc and 690 for phosphorous, Valvoline VR1 10w30 is 1400 for zinc and 1300 for Phosphorous, and Shell Rotella T5 10w30 is 1085 for zinc and 989 for phosphorous. Not a fan of synthetic myself, prefer to stick to conventional. Looks like T5 is synthetic. Currently using VR1, but shell seems cheaper.