My anecdotal experience:
I've run miles-5ks traditionally in flats (Hyperspeeds/Tartherzeals) in the past. Some decent results for me ~ sub 17 back in the day on a hilly course (I'm not good at 5k), 4:47 off not too much training (20mpw, basketball) for 5th Ave Mile ~ I was 20+ seconds faster in my prime.
Ran a road mile TT in the Next% over the Streak LT4s just because my workouts in the Streaks had ravaged my legs a bit, and the Next% were collecting dust with races all cancelled (a mile on the shoes not gonna do anything anyhow). I had no problem running the mile in them and ran 4:48. I suspect I would've ran about the same in the Streaks but my calves would've hurt more after.