BDC, I think something you missed pointing out about the Enkei rims is the width. Find me a 17x5.5 rim, and I'm sure the extra 2 inches of width will save you 2-3lbs, maybe more.
There is no doubt that a 17" band of steel will weigh more than a 15" band of steel given same widths. At some point one needs to decide if an 80 sidewall is appropriate for their driving, or if the 40 sidewall makes more sense. Lots of comparing rim weights and tire weights, as well as where 80% of the mass is located on the combo.
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