hmm... i really wouldn't know where to start BUT if I was to do any insane forced induction upgrading, it would have to be a super-charger.
I've never really been a fan of Turbos, despite how good they might be with respect to tuning capabilities and cool option of blow-off valves additions.
In my opinion superchargers have a nice pull throughout the entire torque band of the rpm range, not to mention the nice whining noise.
haha... I know i am going to sound like an idiot but I am basing my opinion off my current (R53) John Cooper Works MCS and i do apologize in advance for weak justifications.