I have had an 2013 AC 26" for a while and it's superb. It's not light (31lbs) but it rides light and will stay in one piece unlike my last frame.
In the short time I have had it I have done everything from 3800' Munro's and 6 hour rides to very steep and technical Scottish DH courses. It's nothing short of exceptional and build quality/attention to detail is the best in the business.
The geometry they quote seems a bit off to me ie mine is slacker than advertised which I really like. My setup with revelations 150's feels more like 66 degrees than 67 and when the new Pikes arrive shortly it will be even slacker. A bike like this is just so good at everything and if you run proper components and tyres it is fit for anything.
As for 650b I couldn't say as I think it's utterly pointless but each to their own. One thing is for sure, if it's made by Nicolai there will be a massive amount of thought that has gone into it and it will be a superb bike.