If i'm not mistaken, that review is for One X for att, which doesn't have Tegra 3 in it. It does have data for Tegra 3 (One X international version), but it doesn't seem to support the claim that Tegra 3 is more power efficient because of the +1 core.
Maybe not more efficient than everything else out there, but more efficient than if it used 4 cores only - especially at that 40 nm process. I think Samsung's Exynos processor was a bit more efficient, even though it didn't have the 5th core, but it was made at 32nm.