There is definitely no sense in swapping the motor unless the drivetrain is changed as well. With the potentially very high HP the stock motor could produce in a high state of tune, there really isn't a reason either. Given the advanced ECU controls and a properly sized turbo I figure that with some finesse you could get a 280-300hp Fiesta to handle well while remaining front drive. Those power figures are well within the capability of the stock motor. As long as the boost didn't spike down low and you were able to carefully and linearly ramp up pressure, wheelspin out of corners should remain under control. With the stock turbo the torque peaks so early that wheelspin becomes a major issue leaving low speed corners, a slightly larger turbo should move that torque peak higher in the rev range so that by the time you hit full boost the tires will be able to grip instead of being overwhelmed.