There is no significant benefit to a larger filter other than slight (and I do mean SLIGHT) increase in capacity.
Subaru's tend to shed a lot of metal into the oil. What you want is a *better* filter. And better isn't always bigger - smaller micron rating, and things like the number of pleats in the element (surface area), and the type/location/psi of the bypass valve are much more important than the size.
And the Subaru blue filters are straight garbage. WIX is good for a cheap filter. If you want the best - Amsoil or Royal Purple (same manufacturer).
GD