I looked at it and can't really feel the love. I'd not attempt anything with it that couldn't be done with a .223 with 75's.
Saying you can get .250 Savage performance out of a 25-45 is the same as saying you can get .22-250 performance out of a .223. Same capacities involved. I just ain't seeing it with like pressures and barrel lengths.
If I were looking for any performance increase on a '15 platform, I'd be looking at the Grendel case. I'd bet a dollar somebody's necked a Grendel (or a 6.8, for that matter) to .257.
Of course, if you have a big pile of .223 brass and a big pile of .257 bullets (or if you just want to), rock on.
A Grendel or 6.8/Valkyrie case is an improvement but if you want the ultimate in a AR15 type rifle. use a WSSM case. They cut down magazine capacity but make bank on fps, if that's important. I had a Dtech 243 WSSM upper I let go when I shouldn't have.