Almost 50-minute effort so 6.3 w/kg is a lot, especially in TT position (a small fraction of power is lost compared to normal position). You will have a hard time finding in recent years efforts greater than 6.3 w/kg when duration is approaching an hour (maybe legendary PDBF TT but no powermeter

). We've seen 6.5-6.6 w/kg by Pogi on climbs but duration was 20-25 minutes: twice shorter, which enables cyclists to go a few percent beyond FPT.
BTW I'm certain that most of other guys had between 5.5 and 6 w/kg (typical long effort for good but heavy TT-ists)