I am trying to use the cheapest synthetic/semisynthetic for a 7500 mile change for one of my cars. The choices I currently have at Walmart are Valvoline maxlife for 15.88, Quakerstate Synblend for $16.97 and Supertech synthetic for $17.47. It is for a 99 mazda protege with a 1.8 and no leakage. For the next change I am using the Maxlife after rebate. Afterward Would there be any advantage to using Supertech full Synthetic or a store brand synthetic over the cheapest synblend 5w30 I can find?