Speeds may be similar but with the higher flex temp it'll take a lot more runway distance to get to the same speed. Hence the oh ****...
Max flex on the bus is ISA +55.
I've almost done it at the Gold Coast once. Dark stormy night. Tired. TS closing in. Cleared to backtrack. Saw the displaced threshold and almost turned onto it before realising the mistake and kept going. The threat was ATC who gave the backtrack for an expedient departure.
Those in glass houses.