I test drove an M2 when I had my M135i and honestly speaking apart from the M2 feeling much tighter and stiffer I could barely tell the difference, certainly no noticable difference in performance between the two from the 30 odd minutes I had behind the wheel. I suspect on track the M2 would feel substantially better though. I too noticed my MPG improving significantly after about 10-13k miles. It began to drop off again after about 40k miles, but that was 40k miles of any old 95RON fuel. After that I switched to only using premium (BP Ultimate, Shell V Power or Esso Synergy+), and the efficiency slowly improved to where it was at its peak. One big difference between the M135i/140i and the M2 (and the main reason I suspect you are seeing lower economy) is the gearbox. The 135i/140i have the ZF8, which among other significant differences has the coast function in Eco Pro mode, which the 7DCT in the M2 does not have. @Tee Hee Johnson as @Blackhawk47 says Pro Nav is a "must have" in my opinion. I would also look for HK audio. I had the BMW Advanced system, but wished I'd spent the little extra and chosen HK. Luckily I think both options are pretty common in these cars so shouldn't be hard to find. I also chose adaptive suspension, which was great. Soft and comfy for day to day driving, and stiff and sporty when you wanted it to be. Truly the best of both worlds.