Your manual says that 5W-30 is preferred and that thinner oils provide the best fuel economy. It also list thicker viscosity oils and says that they are required to properly lubricate the engine in high temps. There are severe condition recommendations for up to 50 grade oils.
Most Subaru turbo owner's prefer more robust oils like GC, RT6, and oils with an HTHS of 3.5 or higher. Basically anything that isn't Energy Conserving. The 3,750 mile interval became a recommendation from SoA when sludge in the oil screens became a problem. I blew a turbo with just over 20k miles on it (although I'm not sure if sludge was the exact cause) and I always perform uoa's.
There have been a few good Energy Conserving uoa's popping up though. On nasioc (linked above), there were some recent good Pennzoil Ultra and Platinum uoa's. There's also a decent M1 0W-30 uoa posted here (after most of us told him he was crazy) that was run in a Cobb Stage 1 Forester XT. And there's even a good SuperTech 5W-30 posted here from a Cobb Stage II(?) WRX.
You're not going to find many Subaru turbo uoa's going much past 5k though, or even several consistent EC uoa's. I go about 6k and used to go to 7-8k. Subaru has changed the interval on 2011 turbo's to 7,500 miles, but I believe they made changes to the oils screens several years ago as well as did some oil line rerouting in the 2011's.
-Dennis