The bottom line is..if you want high performance, don't get a bog standard mini. They were not designed for sub 10s 0-60mph acceleration, or 100 mph top speeds.
If you want a mini and performance you will need to spend money. Engine technology is improving all the time, the last minis built are now 12 years old so even they will struggle to keep up with a modern family saloon.
Even the so called 'sports cars' from the 60s and 70s can be embarrased by the performance of some of the modern people carriers.
Nearly 11 seconds 0-60 isnt quick at all to be honest. Our works van can do that!. The way modern engines deliver their power has a lot to do with it. Both engines might peak at exactly the same BHP, but the RPM they do will be different. Torque is relative to BHP.
Example - 1275 A series produces 30bhp @ 2000rpm increasing to 70bhp @ 5000rpm. Now pick a 1.3L engine from the manufacturer of your choice. This might produce exactly the same BHP but it already has 45bhp under its belt by 2500rpm. But the 'book' figure will be the 'same'.
The A series will never be considered a performance engine anymore, as the technology is far too outdated.