The lightest wheel/tire combination in the Tire Rack test had the best handling and lap time (which would be expected), but it didn't beat the fuel economy of the stock wheel/tire. That seems odd...but notice the tires used in the test.
Only the stock tires were Low Rolling Resistance. When they tested lighter 17" wheels, they also changed to wider, non-low rolling resistance performance tires.
This test may help illustrate another point:
Don't underestimate the impact of using LRR tires. Dropping weight off the wheels didn't appear to offset the loss of fuel mileage from wider, regular tires. I would think the mileage would have improved if they could have matched the lighter 17" wheel with a LRR tire. That would have been interesting.
People have the same issue running 16" wheels on a Mirage. I don't think there's a LRR tire that will work. Even wider 15" tires are a problem. I don't think there's such a thing as a 195-50-15 LRR tire.
And some of the wider 15"-16" tires out there weigh 5-7 pounds more than a stock Enasave. The weight of the tire is even more important than the weight of the wheel...as it takes more energy to rotate a mass as it moves away from the axis of the rotation.
If maintaining maximum fuel mileage is important, run a light wheel if you can. But don't forget to match it with a quality (and hopefully lightweight) LRR tire.