Do turbos shorten the life of the engine? I don't know- nobody has ever worn out one of these engines. Seriously, the engine in these Volvo's is probably the strongest part of the car. I don't believe that this is a serious concern and bought the turbo myself (S70)when I had to choose.

Why a turbo versus something like Nissan's V6? You need to look at other specs besides HP. For example, Volvo engines are torque monsters and this is what moves the vehicle. The Nissan Maxima engine has 265HP and 255lb-ft of torque, while the T6 engine has 268HP and 280lb-ft of torque. Other considerations include fuel economy, size, weight, etc. I haven't done a compare of these two engines, but to satisfy curiosity you may want to. Turbo's also have a very distinct advantage at higher altitudes, which explains why it was a popular option in WWII aircraft. This is not new or boutique technology.

Plus, you can more easily further enhance the performance of a turbo engine. With IPDs ECU and exhaust you can quite easily bump that T6 up to 280HP and 300lb-ft of torque if you are so inclined.

-Ted