If you only bought it last week, and you chop it in now for a MCS
, unless your dealership takes pity, you are gonna get hosed on the amount of cash you will lose (retail minus trade-in). The moment you drove away, you lost a decent chunk of change - this is just the way of life with used (or new) cars.
So my advice is to get some value out of the money you've already lost, and keep the MC
for 6 months at least, and if you still really find it underpowered, then think about buying an MCS
or something else entirely. Don't forget, MINI isn't just about outright speed - it's also about styling, handling and personality - and the Cooper has all of that.
Chopping it in after just a week would be the madness known as 'buyers remorse'
don't do it !