Do you use highest octane petrol?
I try not to get below 98 octane.

I assume you get plinking at low rpm. Try to avoid anything below 2500 for acceleration.
5th gear is for highway rolling only.
The (my) Sigma likes high revs!

Hannes
once: Green M3W; 2013
now: Red 4/4 Sport; 2011
and some practical cars for use in real life