I'd also be happy with a draw, but there's no doubt a win is absolutely massive. One result keeps us 6 points clear and City still under pressure, and the other opens up a gap that will be very difficult to breach, putting Guardiola in a position he's never faced before.
This was always going to be a huge game but given City's injuries, we need to continue to maximise our points return until they get Laporte and Sane back, and are able to buy reinforcements in January. If David Silva and Rodri are definitely out then that's an added bonus, and if Ederson doesn't play then suddenly their whole back 5 looks vulnerable.
A win would also achieve a lot more than a big points gap - it would represent a shift in power, and maintain our momentum (whilst putting a big dent in theirs). It will also mess with Guardiola's head and may move their focus more onto the Champions League.
In terms of preparation we couldn't have asked for a better week, and with City getting less rest plus letting a lead slip last night, missing a penalty and ending up with Kyle Walker in goal, its all setup nicely for us to capitalise on any weaknesses.