the .264 Win. is within 2 grains capacity of the .257 Wby.(82 grains H20 vs. 84 grains H20). so i don't see huge gains coming from a step up like that, even with the step up to 65000 psi pressure of the weatherby parent case.
for conversation, let's take the 6.71 Lazzeroni BlackBird, a case that has 105 grains H20 capacity and load it to max pressure (63817 psi or 4400 BAR) via 82 gr RE 25 under a 120 NBT. ~3383 fps from a 26" tube.
