Mloclam

Hello all. I have not yet bought my XF and would welcome advice on which model would best suit my needs. I currently drive an old C Class MB which won’t get through another mot. I drive approximately 1000 miles per week, 780 of which are my weekly commute from Glasgow to Bedford. I drive carefully and not excessively fast. I stick to most speed limits all the time but compromise on motorway sections and cruise at 80. My MB returns 50 mpg at 50 mph average over 20,000 miles. Which model is likely to be most economical for me and my usage? I guess I have a budget of 6k gbp and I will put 45k miles per year on. I have considered and discounted the purchase or lease of a more recent model. Many thanks in advance