This won't answer your question, but I figured it would be relevant to the discussion.
The biggest limiting factor to brakes is the tires. Any "upgrades" are simply upgrades to feel and fade resistance. Otherwise, modern vehicles wouldn't need ABS.
If your concern is fade resistance, upgrading to brake pads which have a brake compound capable of withstanding the temperatures you expect to encounter will be the correct course of action. Brake fluid change to one with a much higher boiling point is also highly recommended.
If your concern is actual friction and effort needed to slow the vehicle down, again, brake pads but with a higher friction rating will remedy the "weak brakes" feeling.
If your concern is in regard to extensive repeated high temperature use and fade resistance, then larger brakes is definitely a solution to consider. However, if you are getting to this point, most likely you've got the wrong vehicle of choice and may want to reconsider your choice of vehicle. Thankfully, the knuckles on Subaru's vehicles allow for high interchangeability between Subaru models.
However, any of the original equipment fixed calipers on Subaru models will require spacers and/or new wheels. The only thing I could come up with would be to retrofit the brakes from the 2014-2018 Subaru Forester 2.0XT (SJ chassis) [sport turbo trim level], as they share the same bolt pattern. They would likely fit the 17 inch diameter wheels as older WRX wheels have proven to fit over them.
I would be surprised if you legitimately need this upgrade, as I seem to be the only one in the entire world who would need a big brake upgrade kit the most since I actually drive my vehicle to the very limit.
"Why would I want to profess my feelings for some 3D girl?" - Tomoya Aki from the anime Saekano