The 7mm Weatherby is capable of somewhat more velocity, due to the "freebore" (longer throat) than the short throat in the 7mm RM. SAAMI also allows the 7mm Wby.. a 65,000 PSI Maximum average pressure, versus 61,000 for the 7mm RM. This, plus the 26" barrels often used on Weatherby rifles, often results in a 100+ fps advantage tor the Weatherby.

And as I have noted a few times here and there, everybody "knows" another 100 fps of muzzle velocity makes a VAST difference in "killing power".....

“Montana seems to me to be what a small boy would think Texas is like from hearing Texans.”
John Steinbeck