My fit is a 2020 honda fit sport with 6,100 miles. Been quite impressed on the mpg of this fit. Way better then my 2017 honda fit.

 

Just use regular 87 gas.

Anything mid grade and higher is a waste of money.

 

I found with my fit that i get better gas mileage with mid grade gas about 8 mile per gallons better.

 

Subarus have an issue with valve dirtiness on their 2.0Ts with anything under 93 oct.

I recently switched to higher octane, every now and again add a little TWC3 to keep things filmed up a little.

Non ethanol 90 did wonderful, 93 does wonderful, staying 89+ now. It's only a few bucks extra per fill up but have seen 3-5 mpg hwy increase as well as FAR less throttle needed (see energy density of reg gas vs partial ethanol/octane) to propel forwards.

 

I been using premium gas it my fit. I notice better acceleration and increased gas mileage. Just took at trip and getting 38 mpg at 75mph.
Same trip with 89 octane gas i get 32 mpg at 75 mph. Their is great benefit in using higher octane.