My understanding is that this:
2. during flight approach and section of measurement an altitude between 5 and 35 meters must be maintained. Speed measurement from both directions per flight. The mean value resulting from both fly through directions gives the record speed.
Means the speed run must be done from level flight, not out of a dive. There are lots of prop planes that can break 213mph if they dive (of course I mean lots of speed planes, not lots of planes in general) but very few that can attain that in level flight.
There was an F1 pylon racer that although I didn't see it was supposedly clocked at 216mph at a jet rally last year. I'm sure most Q40's would easily break 220 out of a good dive, with the right engine apparently a Diamond Dust out of a dive could hit that.
So when you ask what the fastest prop plane out there is, it's somewhat of a loaded question, that plane doing 213 on the flat is probably capable of 230 or 240 out of a dive
