Oh, I don't know about that. Power gains, I agree but efficiency? Usually - at the expense of increased fuel consumption to accommodate the increased air delivery.
Mitsubishi has used turbos in the past but didn't here - I'm guessing this is due to agreements with Thailand to build this as an eco-car in Laem Chabang.
Also - we've had more than one report of a failed head gasket. I would be concerned about increasing compression ratios more than what they already are.