The 777/787 are crossing the Atlantic at .84 to .86 unfortunately these speeds are as far as I aware unachivable in the Max and Neo, these types of aircraft crossing the Atlantic are still very much in the minority.
Your going across the Atlantic during peak hours, you will be held lower as you won't be able to get the higher levels occupied by the faster jets!
Also taking off from say Manchester going to JFK the aircraft will be pretty heavy, the aircraft simply won't have the performance to climb up to the higher levels straight away, therefore crossing the Atlantic lower, say FL300-340, therefore burning more fuel.
Yes everything looks good on paper but in reality it's a different ball game...