Hey Izzy.. Welcome to Chinertown!
The bulk of my knowledge lies more with the 057 frames.. I did read up on the 256 to decide that I'd think I'd rather just stick with the 057, for now. I believe the 256 is supposed to be lighter (and that's always tempting) and I did really like the more straight lines of the frame.. For me, it just came down to the fact that the 057 frame has been proven as being a solid frame. It's been on market long enough to have plenty of online feedback from owners.. Also.. I figured this has also given the manufacturers time to perfect the production process for this particular frame. While I'm sure that will also carry over into the 256.. It's just too new and too light for my weight of 210 lbs with riding gear on.
That said, I'd be willing to bet that I could have bought that 256 frame and tried to ride it into the ground and break it and not be able to. People tend to underestimate how strong carbon really is, myself included. It's really up to you if you want to be more of an "early adopter" or not. Odds are, the 256 would be a nicer, lighter option. Especially if your below 200lbs.
Sorry if that wasn't exactly what you're looking for Izzy.. I'll see if I can dig up a bit more information for you this evening