Chuck Hawkes lists the balistics as follows:
Cartridge (Wb + type) MV (fps) V @ 200 yds ME (ft lb) E @ 200 yds
.300 Wby. Mag. (180 Sp) 3240 2826 4195 3193
.300 Ultra Mag. (180 Sp) 3250 2834 4221 3201
He also list trajectory as:
Cartridge (Wb@MV) Bullet BC 100 yds. 200 yds. MRT@yds. MPBR (yds.)
.300 Wby. Mag. (180 Sp at 3250) .483 +2.4" +2.6" 3"@155 320
.300 Ultra Mag (180 Sp at 3250) .483 +2.4" +2.6" 3"@155 320
I never realized how close they were. I own a Mark V 300 Wby but not a 300 RUM. Therefore, I cannot comment on the later but the first is an excellent cartridge and an excellent rifle. With a 180 grain Nosler Partition my father and I have shot large Elk, Whitetail and Mule Deer. If shot well, they usually don't take another step. I recall shooting an elk on the run only to watch it summersault into a cloud of dust, which was to say the least a great experience.
Then again, the largest elk I ever shot was with a 30-06. It is true that bullet placement is the most important, but it looks like both cartridges you are looking at will be flat shooting and hard hitting which at times will give you an advantage, if not only in confidence. Both should be capable of taking any game in North America, except maybe the largest of the bears.
On a personal note, I think the Mark V is one of the best built rifles/actions on the commercial market. Nine locking lugs, and a 54 degree bolt throw. I trust it more than my R93 Blaser which I paid three times the price. This love for their rifles is probably why I own a 257 Mark Five SUB MOA Accumark from the Weatherby custom shop.
Weatherby rifles and their cartridges are a legend and story all to their own. Yes they are more expensive to buy and shoot, but boy do they look good. As their old trade mark said "Weatherby, symbol of Superiority". I don't think that has changed over almost 50 years of rifle and cartridge development.
If you want to shoot a rifle go ahead, if you want to shoot a Weatherby, shoot a Weatherby.