If you're nailing it, it won't be anymore fuel efficient.
They are though...
Look at a 210 BHP 1.8T vs a 200 BHP Mk5 2.0 TFSI vs a Mk6 2.0 TFSI...they all make the same power, but they get more fuel efficient every generation because FSI allows more precise control of the fuel atomisation, giving a better burn, more power and less fuel drop out...so a 1.2TFSI will usel less fuel than earlier 100+ BHP engines.
A Mk6 GTI is at least 5 MPG better everywhere than a Mk5 GTI...and they are both TFSIs...so what are the gains over non FSI engines?