gm 3.6

Hi, I have been running Valvoline Synpower 5w30 Dexos1 in a GM 3.6 LFX. At the moment, I have access to Castrol Edge 5w30 Long Life which is a VW504/507 acea c3 low saps oil. I can get the Castrol at half the price of the Valvoline, so obviously tempted. My concern is TBN retention using high...