I would take 4th place right now. We just don't have the squad depth and I don't see our injury crisis disappearing anytime soon. It's likely that we will plod along till the end of the year and maybe we will have a better run next year in the second half of the season. If the owners do not give Rafa the necessary backing in the January transfer window and next summer, then there is not much further we can go, and Rafa would be wasting his time here. Too many clubs have caught up with us and that has become hugely apparent now.
As is often the case, sides are overrated on their early season form. Every season sides fall away badly or pick up almost twice as many points in the second half of the season as the did in the first half.
I reckon Arsenal won't be good enough to sustain a genuine title challenge and will probably be 10 points off the pace at the end (give or take 5 points). Man City and Spurs won't win the league and are both inconsistent enough to finish as low as 8th-12th. Spurs could do 4th at best, Man City 2nd at best. But the potential for spiraling down the table is there for both Spurs at Man City, so a lot will have to go right for them to finish top 4.
Quite a bit would have to go wrong for Chelsea or the mancs to finish outside the top 4. Most likely these two are going to finish top 2. Their bad runs will be shortish, and their good runs potentially very long.
Villa are a good team but will again struggle to compete at the level needed to finish top four for the entire season. They haven't improved enough on last season to make that jump. Everton are in the same boat and have had a relatively ordinary start to the year.
As for us, in terms of picking up points, we can't do too much worse than we currently are. If you include Aquilani in our best side, we haven't had it on the park yet and won't until December. It won't be until probably February (at best) that we have our best defenders (Carra, Agger Johnson), midfielders (Masch, Lucas, Aquilani, Gerrard) and attackers (Torres, Yossi, Kuyt, Riera) all ready to play at the same time. That leaves plenty of improvement.
I don't think we'll win the league, but there are a lot of things that can and will turn around for us. Continuing our good run against the mancs, Chelsea and Arsenal from last season would also be a nice way to keep within a reasonable tally of the top.