actually everytime u change to another brand of petrol, ur engine ecu will take some time to adapt to it. u must refill the petrol for 5-6times then only u can determine whether the petrol provide better fc.
the first tank after u change normally give u worse fc...

correct me if i am wrong...

i use to pump shell and petronas, i would say shell is better in terms of performance, and if u can control your right foot, u shud get better fc with shell. Petronas give weird noise and pick up really not that good.