I'm considering changing one of my F-Open .284 to a 6mm of some kind. A lot of choices out there: 6mmBR, Dasher .243 Win, .243 AI, 6 PPC, BRX, BRBS and BR-DX, just to name a few. Will use the rifle at F-Class Mid-Range - 300, 500 & 600 yards. The action is a Bat. Would like at least 2500 round barrel life. Which 6 would the expects recommend?