As far as tuning goes, my preference is the Synergy 2, it is plug and play, a Pierburg MAF (Mass Air Flow Sensor)
is a must and can be bought with the Synergy to save fiddling with the Bosch MAF
settings, I have a Pipercross air filter that although not much, makes a difference also to me. A Synergy kit will set you back £300, no better or worse than a remap, but a remap cannot be unplugged/switched on/off, used on any 75, or taken off and sold. My Synergy has been on my last three 75's, I used to change my 75 every other year at least, so plug and play suited me best. More power = less throttle, so I have never noticed a difference in mpg. You will be very impressed with whichever tuning route you take, to me it is not just the throttle response, a standard 75, especially 116bhp, feels like it has a clogged air filter and unhappy.