I don't think there is a dark horse here, not in terms of who could win. McLaren will dominate in S1 and S3 while Red Bull will easily dominate in S2 (the most important sector really, given that Red Bull now have their own duct working nicely).
That said, i think Williams could spring a surprise and get amongst the top 3 teams... they should have new Cossie engines in for that race.
So you think Williams for the dark horse?
I think Force India... Sutil to be precise.
But like you said, not really to be on the podium or to beat the big guys. But at least to be best of the rest.
Dont see S1 and 3 as clear cut Mclaren dominating... Maybe because of the Merc engine, but it could depend on how much downforce they end up running so as not to lose everything in S2.
S2 is Red Bull's... unless they run some huge compromise to get some advantage in the other 2 sectors.
To me S1 and S3 are for Mclaren and Ferrari to deal it out.
Came out fighting indeed.