[brucepick]

I think you're right in that there might be a slight advantage in a slightly larger moon hub cap on a wheel/tire combination with same final outer diameter. However don't think the extra inch diameter would make that much difference.

You should weigh the two wheel/tire combinations and see if one is heavier. Tires are rotating mass and depending on who you read/believe, any additional mass will work against you 2x to 3x as much as if it were non-rotating mass. That's especially true for any driving where speed varies. Go with the setup that weighs less.

The "rotating mass" reduction thing is what originally drove performance enthusiasts to mag wheels and alloy wheels. Has nothing to do with bling - that came much later.

You can look up the weight of current available tires at tirerack.com if you need to. It's under "specs" for most tire make/models.