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UPDATED: 09/27/15
After 3702 I decided to pull the filter and take a look. As a side note.. I use to religiously change my oil every 3k miles.. but with the advancements in oil and filters even someone with mechanical OCD can push it a little further... dare I say... 5k? ANYWAYS. After driving the car and then letting it set 10 minutes to allow as much heat soak as possible. The highest temp taken from the filter housing was 94C/201F. This is very acceptable. Of course.. this was not taken during any type of rally event so temps could possibly get a lot higher. For now.. I am going to enjoy more filter media in my filter unless a problem arises from it.
Using a H6 oil filter on an H4 engine.
Note: I have been reading some things that suggest the fact that Subaru intentionally made the filters smaller to avoid heat from the exhaust manifold. I can not confirm this myself, but it is very possible. My 2010 Impreza non turbo sure had exhaust that was tightly wound around the filter.
So.. I have always been a fan of using the biggest oil filter possible. This time when I was at the store to buy an oil filter, I started looking at what other options I had. I have always used the Bosch D3300 as called for, but there is also a D3312 for the H6 engine. The threads are the same, the diamater of the filter and gasket are slightly larger. Looking into the filter, there is a lot more filter surface area, as well as what looks to be much better flow. The only deal breaker is the bypass valve pressure. After doing some research I found that the specified bypass psi range for both filters overlap each other, so this D3312 should be safe to use. Here are some pictures of the differences.