I have 13 rifle chambered in 257 and the 700 CDL-SF parts gun is my favorite. Rather than spending $$ to have your chamber recut and buy a set of 257AI dies, I think that you would get more value by using that $$ to have your barreled action bedded in a McM stock in your favorite style. My 700 CDL-SF is bedded in the McM McM Hunter style and changing the stock has made a "night & day" difference in how well it handles.
In addition to the 13 257s, I have a few 257AIs and 25-284s. While both the 257AI and 25-284 are faster, I don't think that either is enough faster to make a meaningful difference, because of the slightly flatter trajectory, in the field.
