From the above thread:
Q: SR5 -
Warm climate, family car, do you go a Group III 5W30 synthetic for a bit more coin, or a Group II 15W40 A3/B3 mineral for a bit less coin ?
For the Group III 5W30 synthetic, would you select the A3/B4 or the Dexos1-Gen2 version, given the same price ?
A: Joe -
Group III 5W30 (presumably A3/B4) or Group II 15W40 A3/B3? For me, the 15W40 is the better lubricant. Reasons are lower Noack, less VII, marginally more ZDDP & possibly less ashless dispersant (not that big a deal for gas engines, more significant for diesels). Also Group IIs are 'greener' to produce than Group IIIs. Also I'm notoriously cheap!
Group III 5W30 full synthetic A3/B4 vs dexos1-Gen 2? For me, the A3/B4 oil wins BUT these two are so close, there's not a lot to differentiate them. I'd opt for the A3/B4 oil because it HASN'T been put through the US fuel economy tests. I don't like these tests because as often as not, they 'encourage' formulators to drop the oil's CCS viscosity to silly levels to cheat the test. Lower CCS means more VII & higher Noack. The A3/B4 oil might also have a higher ZDDP content (but not guaranteed) & a higher TBN.