Greenfield had a blip of wind over 300 mph but it wasn’t sustained like some of the others. As mentioned already that Bridge Creek monster back in 1999 was a nightmare.
The Iowa greenfield tornado was not the strongest in history that title goes to the 1999 bridge creek Moore tornado at windspeeds of 321 miles per hour while greenfield had 318 miles per hour
Those windspeeds are the max winds derived Greenfield had a higher minimum windspeed than Bridgecreek, at 312 over 302 But Bridgecreek is contextually stronger damage wise, max wind, and highest wind duration wise. But that doesn’t nor shouldn’t devalue the absolute might of Greenfield