Havertz and Rice should rotate in the 8 role depending on the quality of competition we're facing. On reflection, I think Rice will struggle as a 6 for the same reasons that Xhaka did, as he isn't nimble or agile enough to evade pressure and his passing isn't quick or sharp enough to beat the press. He looks like someone who can evolve into an effective 8 as he's strong at carrying the ball and in his combination play. His effectiveness around the box is still unknown but the highlights from the Monaco came were promising where he created a key chance and almost scored.
Havertz on the other hand looks like a throwback to Ozil and Ramsey with similar issues in terms of positional discipline,. Whilst, he's good at identifying space and running into it, his over focus on this means he's always too high and out of position in defensive transitions. Furthermore, he lacks the intensity to track back hard and recover position. Note how Xhaka was also occupying high spaces but was seldom out of position, and when he was, he would sprint back and get onside.
Partey and Jorginho are both better than Rice as 6, but Rice is more solid positionally than Havertz as an 8 whilst still offering offensive impetus, so for those reasons I would start the following team against City
------------Ramsdale
White--Saliba----Gabriel---Timber
--------------Partey
-------Odegaard--Rice
Saka--------Trossard------Martinelli
