Welcome to the forum Duncan. Sorry I'm late reading this thread but you mentioned a rubbing on the left lock?
Check with your local dealer and see if your car had a re-call for the steering rack ( also check the back of your service manual for any recall codes ). I had an 05 Tornado Red DSG with a "Grinding" sound on full left lock. I remember discussing it on another forum and found many other owners had the same problem. I think Red Robin also had the recall.
I was under the impression that the issue was resolved before your model year though.
As for your MPG dilemma, I often only manage 270 - 280 per tank
although I do commute on a terrific bit of A road every day. My previous R32 was only managing 19 MPG.