Mk2 Mondeo 2.0 - 130bhp
Mk3 Mondeo 2.5 V5 - 170bhp [+40]
BMW e39 530i - 231bhp [+61]
BMW e39 M5 - 400bhp [+169]
BMW e60 M5 - 507bhp [+107]
530i to e39 M5 would be the biggest upgrade in terms of power, although given they were such similar cars, the Mondeo Mk3 -> 530i felt the bigger upgrade in terms of overall package.