Were I in the market, my decision would come down to driveability, but based on specs, I'd choose the turbo over the (existing) V6:
"a 3.7L V6, putting out 273 hp at 6250 rpm and 270 lb-ft of torque at 4,250 rpm". And that's in a 4500 lb car!
The lighter weight of the 2016, and the +40lb torque should mean better acceleration.
I'm betting that in a Mazdaspeed, this engine will be tuned for a better top end.