New windshield wipers. Bad ones get *really bad* at 115mph in the rain. Being unable to see makes things more difficult. I don't think it matters what brand, as long as they are relatively fresh and in good condition. Smoothen all steering, brake and throttle inputs.
Think about this, most Subarus are not traction limited in rain under acceleration. You'll still be able to build up speed in a hurry, but you have to slow down more for turns, and it will take longer to do so. Brake early at first and feel how much grip there is in each corner. If I have a pace lap and nobody else is right on my bumper, I'll try to traction-sample each corner by picking out however much steering I need to get through it, then wiggle the wheel around maybe adding 5-10 degrees extra steering lock while at constant throttle. If the car understeers/pushes, you know it's slippery there, and you need to be extra-aware. If not, there's some grip there to work with. Try some different lines, you'd be surprised where you find grippy pavement. Sometimes it's on the inside of a corner exit where nobody normally is in the dry, but it gives you nice rough pavement to grab onto. Shiny pavement=bad, matte black=good usually. Standing water=bad, wet pavement=less bad.
I keep a couple rags in the glovebox for the aforementioned "wet shoe" issue.