Having discussed the Mig 23 handling characteristics with a test pilot who flew many hours on the jet, I can safely say that no Flogger pilot would have risked anything remotely close to 900 kts at low level. His words were he spent most of his time on the aircraft trying to prevent it from killing him. The aircraft had some very nasty handling characteristics.
Ironic as we were all paranoid about its capabilities when it sat over the border from us during the Cold War. If only we'd known.