[sperry]

I think a lot would have to do with the actual build on the race motor. A motor built specifically for racing where it's only expected to last a few dozen hours between rebuilds probably won't last as long as a stock motor as a daily driver. But I would guess that most "built" motors, ie motors that have forged pistons and good bearings but is otherwise built to relatively stock tolerances, will likely outlast an OEM motor on the street, if only because subarus' these days aren't exactly the longest lasting motors, at least on a stock tune.

As far as mileage... any built, high horsepower motor should theoretically get better mileage if it's driven conservatively. If a motor makes a ton more power, it's because the volumetric efficiency of the motor has been improved. So that should mean for better mileage. However, the reality is that a) generally no one will drive conservatively enough to counter for the times when they let it rip, and b) there are likely tuning differences to make the engine safe at high power levels that will hurt efficiency when driven conservatively, ie extra fueling for cooling, big injectors that idle rich, etc. So in practice, I would expect worse mileage in general.