I think it's 8 points but since they have one more game than City, that means as long as City wins that extra game, the difference is still 5 points and nothing really changed aside from getting one more game closer to finish line.
Only ten games left. Even if Manchester City win the missing game and decrease point difference to 5, that means Arsenal have to slip in two games and City don't make any mistakes. It doesn't look like both teams make a mistake though. Both teams will play with Liverpool and Chelsea and they play with each other. There is no fixture advantage for any sides. I still believe Arsenal will go until the end and lift that long awaited trophy.
Though it wasn't between arsenal and Manchester city, I can recall that this same thing happen in 2012. Where Manchester United and Manchester City we're having a very close points. Manchester city with much goals were favored.
I'm making this analysis based on the current situation on ground. Manchester city hardly gives up when they have come this far, and will not give up this season especially now that arsenal isn't far from them in the standing. In favor of Arsenal I pray what happens in 2012 doesn't occur this year.