Sometimes when he races ultras, there's a sense that Kilian runs most of the way pretty comfortably with the best of the others and then picks up the effort towards the end to get the win. With his BGR being a record attempt, I think what we saw was more or less his limit on that day and I think it's one of the strongest FKTs.
Enough people have done the BGR to give us a decent idea of how good the time is. True that not many of Kilian's calibre had taken a crack at it but then there aren't many of his calibre over that kind of course at all.
It would be interesting to see what time Kilian could do for the Wasdale Fell Race (not an ultra but 21 miles with 9000 feet of ascent). Billy Bland still holds the record, set in 1982, and it's stronger than his old BGR record. Nobody gets anywhere near it these days.