Is it worth reducing the cars weight by 45 pounds... by...

Octane is a measure of how well the gasoline resists knock. Which is the detonation of the fuel air mix from pressure.
Higher octanes tend to have slightly lower energy content, but modern engines can advance the ignition timing some to compensate for that. So I think any changes the higher octane has on fuel economy would likely be lost in the noise of other variables.

A note for other cars. The manufacturer is free to list a lower octane as recommended than what the engine can take advantage of, and will do so when a premium listing will hurt sales. The 1.4L turbo GM uses in the Sonic and Cruze, will get better fuel economy with higher octanes. Just not enough to justify the price increase in my experience.

Also, the EPA test blend is 93 octane w/o ethanol. It's 91 for CARB.