It's a light car, and you don't need that much braking force - the JCW 4 pots are overkill anyway TBH. Also you really don't want to increase unsprung weight as that's where weight is most critical. Big calipers are heavy.

JCW 4 pots, direct fit, and DS2500 pads are all you need IMO if you want bigger calipers. Remember that the Time Attack R53s & R56s ran on stock R56 calipers, due to weight. They had plenty of braking force with the right pads and didn't limit choice of wheels, like bigger calipers do