If 10W40 QS Defy and Mobil HM 10W40 are serving you well, I don't personally see a need to switch to a different brand.
I'm not familiar with your particular motor, but I have a flat tappet cam in my stock 97' Ford 460. I've used Mobil 1 HM 5W30 for quite a few years and my motor is still "Strong like Bull!"
When Mobil changed the HM 5W30 to an SN rating, I was concerned about lowered ZDDP. The most common answer I received here was the spring pressures on my particular motor aren't enough to require extra ZDDP levels.
I then asked my Mechanic, who told me he has 3 or 4 other regular customers with 460s, that all have over 200,000 miles on their motors. The most economical oil he offers to his customers is VWB, and that's what each owner has been using in their motors for years and years, without an issue.
I'm not familiar with your particular motor, but I have a flat tappet cam in my stock 97' Ford 460. I've used Mobil 1 HM 5W30 for quite a few years and my motor is still "Strong like Bull!"
When Mobil changed the HM 5W30 to an SN rating, I was concerned about lowered ZDDP. The most common answer I received here was the spring pressures on my particular motor aren't enough to require extra ZDDP levels.
I then asked my Mechanic, who told me he has 3 or 4 other regular customers with 460s, that all have over 200,000 miles on their motors. The most economical oil he offers to his customers is VWB, and that's what each owner has been using in their motors for years and years, without an issue.