You have to see: the Sauber is superior in raw speed. They've started once from the front row, three times from the second row and twice from the third. FI has one start from second and one from third row.
Depends on the track. Any stop&go-lots of slow turns circuit will favor Force India by far. Nice flowing circuits like Spa/Suzuka/Monza favors the Sauber also by a good margin.
Additionally Sauber is better to the tyres in race.
I'm very pleased with the drivers at FI so I wish them a better seat. Despite I want to keep them too =) but it shows good work, if they are considered by better teams