Theoretically, even Newcastle can win the Premier League - as we can see, they managed not to lose to Arsenal and City and, along with Arsenal, have only one defeat in the whole season. But the likelihood of Newcastle or United winning the championship is, of course, very small.
It seems to me that there is not much difference between third and fourth place - the most important thing is that a ticket to the Champions League allows you to hire ambitious players. So if Newcastle and United stay in the top four we will see their activity continue in the transfer market (especially I expect surprises from Newcastle).
I don't see any chance for Newcastle winning the Title honestly, but Man United will give a real fight for the Premier League Title. Things will change for Arsenal if they lose two matches or even a couple of draws will be costly for them. Though Manchester City is seven points behind Arsenal they also played one match less than Arsenal which is a plus point for them. First and second positions of the point table will be decided in the next round when these two teams face each other, maybe for New Castle it is also a fight to stay in the top four.
Its funny how everybody expects Arsenal to drop points and get displaced from the top. I think this is just because they shared a point with Newcastle and Manchester United won their game to move to the top 4 zone. Football is funny at times, games you dont expect them to win are the ones theyll get maximum points from. Likewise Newcastle United, theyve been consistent this season and if they continue with that momentum, I dont see them dropping down any time soon.