I would like to share some of my input that I've been able to "log" with 2 simple devices: an OBDII scanner along w/ car scanner app for iphone, and a dragy perf. meter...
Coming from a car that RECOMMENDED 93 octane for better performance, and doing some "research" on the 1.6t engine prior to buying the Forte, I decided to continue on w/ fueling up w/ 93...
Did a few runs/pulls 0-60s, 45-65, 20-60, 80-100 mph plus a few others, 1/4 mi, 1/8 mile...cool. Quick car.
After 2 1/2 months of fueling up w/ 93, I decided to try out 89 octane...
There are NO differences between 89 and 93....at all. None that dragy can show. Taking into account variations in temperatures and DA, of course. I am at sea level.
Back when I was running 93 octane, the car scanner app "logged" 226.76 hp @ 55F, on 89 octane the app logged 221.65 hp @73-77F... Granted, I do not know the accuracy of the OBDII scanner in proving engine HP, seem pretty accurate for other values I occasionally track, and 220-227 at engine would equal ~182-192 at the wheel...
I don't know if there are any differences between the 2020 and 2021 Fortes, (I don't think so), but at least that's what my '21 is showing me.