Bruno28, You would enjoy what the F20 125i M Sport has to offer over the previous model in its drivability, but to get the best from it, you need to add 'Sport auto' and 'M Brakes' and that will set you back around $65k on the road.
You will then be tempted to add other goodies like HK sound, Xennons etc etc
The 125i's engine and 8 speed auto with paddles work exceptionally well together.
The rumours are that the M chip will be released for the 125i and 135i soon and that could take the 125i from 163kw to over the 200kw and give a sub 5.
The 125i is quick as it is. I think the real 0-100 time is closer to a flat 6.00
If you have to have the sub 5 seconds, save your money or borrow more and get a F20 M135i or second hand M1