force india has good aerodynamic efficiency, which helps on fast tracks, and also the mercedes engine which helps even more. but they dont have much downforce compared to other cars so are slow on other tracks. a couple races ago they got a major upgrade to the car, which seems to have also helped, we can see this with current in season testing ban, some cars may make unexpected improvements and otherwise go backwards with new parts like brawn did.
mclaren have through out the year had bad aero efficiency, which makes them very slow through fast turns, but have shown to be good at high downforce tracks like monaco and hungary. but they have the advantage of mercedes engine and kers. In spa we saw, they were very fast in sector 1 and 3 (similar to how the whole monza track is), but they failed in the sector where there was high speed turns.
mclaren have shown to be good at high downforce tracks like monaco and hungary, but remember they didnt show it in monaco because hamilton fluffed it in qualifying.
But also mclaren also have millions of dollars, and they have probably fixed their aero problems, i thought they would would slow through the lesmos, but its not so anymore, and through the parabolica hamiltons car looks more stable then anyone elses, so go figure... its been an interesting season.
I dont think Fisi is kicking himself, i dont think force india will be so fast at any of the remaining races, but ferrari should be. He is living his dream, and he has a chance of points at monza in a ferrari, he has even said he doesnt care if Force india win the remaining races, he is happy to be at ferrari and try his best their. he already has race wins in his career, i think to him a win in a ferrari is a better goal then a win in a force india.