"If I was to ever buy a Subaru I'd buy a 6 cylinder and enjoy the extra power and live with a bit less mpg."
That was the philosophy that caused me to select the six-cylinder model when I bought my '02 Outback.
The difference in gas mileage between that car and my '97 Outback (4 cylinder) was exactly 1 mpg.
In exchange for the "penalty" of losing 1 mpg, I got an engine with a timing chain instead of a timing belt, no head gasket problems, much better acceleration, and lower noise levels in the passenger cabin.
With my 2011 Outback, the six-cylinder engine's mpg "penalty" is a tad higher, as it is rated at 4 mpg less than the comparable 4-cylinder model in both city and highway driving. However, to be able to accelerate effortlessly onto a high-speed expressway while averaging 23-24 mpg in mixed suburban/highway driving is worth it to me.
I have been able to eke out 29 mpg on the highway, although 27 mpg is more typical for highway drives with the six-cylinder engine. And, the noise level in the cabin is FAR lower with the six, due to both the larger engine size and the fact that the 4-cylinder engine relies on a CVT, while the six uses a "conventional" 5-speed automatic.