I know you have aneed to have some thing no one esle had, but I would go with the 5.6X285, The bullet selcetion is really good. 107gr up 142's. Laupa Brass. Order a reamer (most people have a 6.5X284 reamer).
The 25.X284 would really smoke a 115 berger out there and be plunty at 600 yards.