I have heard a lot of people say that the ackley design is not worth it. I feel that is 100% personal preference. For some it may not be. I run a .260 AI, and the only pressure signs (as stated) I get are at max pressure. I am running the 156 at 2920 fps, I could run it up to 3000 fps but best consistency is where it is at. Essentially (with a 29" barrel) it gets 6.5x284 performance out of a .260 case.
The people that said twist and improving a cartridge will cause you immense pressure issues likely haven't done it and don't know what they are talking about, because in the several improved chambers with tight twists I run or have loaded for that simply isn't true. Only pressure signs come at max load. Don't expect to gain 300+ fps, but you usually gain 100-150 fps or better depending on the improved design, and you also get brass that doesn't need to be trimmed near as much. In 12 fireing I trimmed my lapua .260 brass once, maybe twice. Few enough times I don't remember doing it. With my Peterson SRP brass, I'm on 5 fireings, haven't needed to trim ot yet.
It does require special does and fireforming, but when I think of fireforming, that just means I get to shoot more.....why would I complain about that??? Ha ha