If you're not extending your OCI's beyond 7,500 miles, there's no advantage to using synthetic in an n/a Subaru IMO. There's also no need for an xW40 either.
I'd just use Pennzoil conventonal (Pennzoil Yellow Bottle) 5W30.
And note that bluesubie makes a good suggestion, too. There's not "one correct" way to do things, really. I've used 5w-30, notably PYB, in my G37, for instance, for a long time, and switched. Following the 5w-30 specification is completely acceptable and sensible, and also a valid year round choice.