You say you will be using forged pistons, what ones? Like I said flat tops aren't ideal for a turbo motor because they retard the flame front. Using a piston with a dish, even though it decreases the CR slightly will provide better low speed running conditions. If you were going to deck the block and skim the head it will need to be blueprinted and use some play doh or similar moulding device to measure your piston to valve clearance, then you can determine how much you can skim off the surfaces without the valves kissing the pistons. Personally I would just go with Wiseco dished pistons and a 0.6-1mm headgasket. The extra torque you get from the 5E you wouldn't even notice a great difference in increasing the CR.