Using Fram as an example for Subaru applications a poor one, imo. Unlike many other filter manufactures, including but not limited to Wix, Purolator even topic AZ STP, Fram makes no distinction for Subaru vehicles and/or higher bypass psi. They rec their standard 7317 series used on many vehicles besides Suby. While you would be covered with a filter warranty on the Fram with 7317, not so with the other filter makers mentioned. AZ STP (no XL option) like the others, has a separate Subaru application. That being the case, the STPXL for the Impreza would have no filter warranty, if something happened no coverage. So as noted here, best not to run the STP 6607XL.
All that said, when it comes to other vehicles the shorty 6607 and .75" longer 7317 generally speaking interchangeable. In fact, many quick lubes and low tier filter lines consolidate to the shorty. No saying that's my preference, just what's done. If it was just a matter of subbing the STPXL 6607, for a 7317 application, especially on out of vehicle warranty I'd see no major issue.