Sierra show a BC for their:
.257 100 gr. Matchking between .376 and .386
.264 142 gr. Matchking between .575 and .580
BIG DIFFERENCE!
Usually when building a custom LR target rifle you;
first pick the bullet,
then pick a case that has enough powder capacity to keep the bullet super-sonic to the max range you plan to shoot,
and only then build a rifle to shoot it accurately.
If other bullet manuf. have this much difference between their .257 and .264 diam bullets I can see why the .264 is so popular for target shooting.
The 125Wildcat runs about .585BC. I mentioned that because the subject was 25 cal. bullets.
However, concerning other calibers, I know of some 6.5 bullets coming out that will be great, the 6.5 is one of the best choices for a target rifle.
The problem I see with the 257RobAI is a lack of cap. for bullets 125 & over, it could work with a 1-8 twist barrel for the 125. A more conventional twist would handle the 115Berger. The very best rounds that I know of to get that balance of a small powder cap. but yet propel good BC bullets good enough for 1,000
yard shooting is the 6mmbr & the improved versions & 6XC & the 6-250. The 6mmbr can be competitive at 1,000yards with 30gr. of powder. I don't know anything else that can do that.