I've just completed a 3 day camping trip to Snowdon, North Wales in my S3. I covered 734.3 miles in total, a mix of motorway (about 350 miles in total), the rest being on A and B roads. For 440 of those miles, the car was packed with two people and camping gear, for the other half, 5 people. Speeds were not excessive keeping pretty much close to legal limits. Below is the read out from the trip computer, which has amazed me! Fuel used was Shell V Power - it's the only fuel i've put in the car since new.