Is there really a need to go to 400 HP? If you want to spend a good AU$20-25k on a forged reinforced crank, bearings, pullies, forged rods and heads, fuel pump, FMIC, by all means go ahead. 400 HP would have torque steer pulling you all over the road, so straight line starts would be a nightmare.
IMO I would rather stick with 270-280 HP, and reduce unsprung weight to get off the line quicker, and without massively reducing the lifespan of your MPS.
For 300kW (400HP) atw, get something with that stock. It might even be cheaper than an MPS + mods cost. In Australia (i hate to say it) but I'd buy a Ford XR8T or Holden Commodore HSV. And if i wanted to mod a car up to 400 HP, i'd go buy a stock Evo 9, and mod it to hell - knowing that this car is tried and tested at that level. IME, the MPS is not a good platform to mod to the level you're after.