It's stretching the the parameters but I believe the first batch of tropical Hurricanes with the Vokes filter were struggling to do 300mph.
Yup, what's worse was that the first Hurricane Mk.Is that arrived with Treble One Sqn in 1937, with their big wooden fixed pitch props and fabric covered wings could barely make 280 mph going down hill, even though the Hurricane was supposed to be the RAF's first 300 mph fighter!