Here is what I have found after driving my RA for 6 months.
Mitsu has really tightened up the ECU programming so that you can't mod anything without reflashing.
The MIVEC head is noisy. When the motor is at full operating temp, the valve train rattles. (the dealer say they all do it which I call BS but I don't have anything to compare to).
Other than that, I would bet that the 4G and the 4B stock turbo blocks w/stock internals will handle about the same power.