After 2 tanks of Shell and Texaco 95, put Texaco 97 in at my nearest station that does super unleaded. Throttle pick up doesn't improve instantly through the rev range. But the low speed 2nd gear knocking noise through drivetrain at 10mph has gone as it always does. Only saved £3-£4 with cheaper stuff. As done purely motorway miles since Wednesday afternoon, economy worked out at a record for this particular car (44.1mpg). Foot to the floor locally expect this to drop by a third next week.