When they first announced the Mazdaspeed 6 I was hoping they'd go with a 6 cylinder engine - Get the power without having to drive the hell out of it. A turbo'd 4 would have been good for a Mazdaspeed 3, IMO the 6 should have gotten a 6 cyl. Nice car, but it would have been nicer with a little more relaxed powertrain. There are already plenty of high strung turbo 4 options out there - Evo, WRX/STi, SRT-4, etc.
There are other options I'd consider if you're willing to spend that much money.
Legacy GT would be a nice alternative.
Viper GTS