I run a 25x300win mag which is a step faster than the 257Wby , and while it is a flat ass shooting round out to about 500yds the 25 cal bullets run out out gas quick , nobody realy makes a decient hunting bullet for the quarter bore and in the long range game ballistic coefficient is what's counts in bucking the wind and holding energy on target , this is why shooting a 115gr ballistic tip out of the 257 Wby at 3300 fps beats shooting a 75g at 4100fps , at 500yds and in the light pill wins but it drops speed and energy fast so it peters out.
the 50 BMG is the renouned long range hammer , it's velocity with a 750g slug is only 2650fps about the same as the poor little 308 but the bullet has a BC of 1.1 where the 308 is .502
I you want realy flat shooting neck a 408 chytac case down to 338 and Ackly improve it , shoot a 285g Henson bullet with a BC of 1.2 out at 3400 fps , you can cleanly take deer to 2500yds but your talking a $12,000 rig once you put decient glass on it