The 6.5-300wby is essentially a full length .264 win. mag.

speaking of, I'm not sure what action lengths weatherby uses on their 257wby rifles, if it can handle the 6.5-300, if not, a re-barrel in .264 win mag would work.

You might want to check out the 26 Nosler, 28 Nosler, 30 Nosler...

Kind of wish they could make the 6.5 WSM work... I hear good things from the 7mm WSM as well, but it appears the 270wsm and 300wsm are the 2 that are here to stay...