Im not sure craig? I didnt go for the Tdi S in the end , mine is the 98 bhp version. I can get my short term trip mpg puter upto 74mpg by driving carefully on a short run,say 8 miles. This involves not reving over 2000rpm. If I drive however I want it does around 54 55 mpg. The real "total" average however is sitting at 56. I suggest that you try drive watching your instantaneous mpg meter and you will be amazed at how you can drive more economicaly by being in the correct gear all the time looking ahead etc, no hard acceleration. The above doesnt always mean driving like an old person either you mention that at 70 the boost is on in 6th. Maybe try dropping to 60 mph for a while and see if it makes a difference? however dull it may seem. just some ideas , im no expert