What you might also want to experiment with, is the "Super" version of the petrol from say BP, AND Shell. Try both!
Reason I say this, right after buying my FR, I went and filled it up with a tank of BP Super - however, the car immediately felt dead, and lacked alot of the power I experienced on the test drive.
For the next full tank, I switched to the Shell equivalent of their Super fuel - and the car immediately came alive again, felt alot pokier, alot more power, as it should!
So I've stuck with this.
So strange it may sound, but you might want to try different garages too.
I'd keep away from the "supermarket" fuels, even if its stated they get their fuel from the same 'Tanker' ! You dont know what other additives might also have been added after.