I have loaded for a straight 6.5x55 Swede and a 6.5-.284 Norma. With 140s, I got 2900 from the Swede. And 3000 from the 6.5-.284 Norma. I would think the 6.5x55AI would match the 6.5-.284 Norma. But you will have 100 or more rounds down the pipe just in fire forming loads.
What I have been doing with fire forming loads is same as regular load development. Do a load development and get a good shooting fire forming load, and once I get 25 or so fired cases, start on that load development too. Usually, out of 100, I have 50 or so cases left to fire form, but I load them up and use them for varmint hunting. And have 50 or so fired cases that are full power loads of twice fired brass for hunting. That way, you don't just shoot them to shoot them.