The full syn looks backwards to me, most 5w30's don't make a cst@40 of 58 much less a 10w30.
I think the synblend is right, yes it would be the VI's but the 10w30 would be more shear resistant so it would likely be thicker as you got into the OCI, JMO.
Good oil, Autozone has it on sale I want to try some myself.
Actually your're mistaken.
You're comparing the kinematic spec's and you should be comparing the HTHSV and VI.
Their 10W-30 has a HTHSV of 3.1cP vs 3.0cP for the 5W-30.
That in conjunction with the higher 167 VI of the 5W-30 vs only 154 for the 10W-30 makes it a significantly lighter oil at all oil temp's.
Both are within the 30 wt viscosity spec range, and a difference of 0.2 cSt is not meaningful. The spec range is 9.3 to 12.49 centiStokes @ 100°C. The high shear rate viscosity @ 150°C for a 30 wt is anything above 2.9 mPa. You made no mistake. The real test of any oil is to check the conditions of the oil after service, say 5000 miles, and see how it compares to the specs. The initial specs may have no relation to how the aged oil protects your engine. The API and ILSAC tests of the oil do run it to test limits of specified hours in test engines to provide aged oil specs.
Ken2, this has nothing to do with new oil verses used oil. What you don't understand is that the simply kinematic viscosity measure doesn't take into account how different oil chemistries behave in a operating IC engine, particularly oils with different polymer levels. The HTHSV measure does, and since the change in viscosity at higher temperature levels is virtually linear, the HTHSV spec' trumps the KV100 spec' when comparing the operational viscosities of different oils.
This point was discussed in detail in the following thread: