Chuck Hawks covered my sentiments here nicely...the math doesn't make sense. If you're buying a weatherby for longer, flatter shooting, you're not getting much benefit for the cost in $$$s and pain.
He writes:
But there is a perceived need on the part of some hunters, no matter how unrealistic, for an even flatter shooting, longer range rifle and cartridge combination. Unfortunately, while there are a few cartridges that can extend that plus or minus 3" point blank range somewhat, it is surprising how little maximum point blank range (MPBR) can be gained without either holding over the target or allowing a mid-range rise which may result in over-shooting at intermediate distances.
A careful perusal of the ammunition manufacturers ballistics tables and the popular reloading manuals reveals that the best of the (at lease moderately well known) ultra-long range cartridges appear to be the .240 Weatherby Magnum (100 grain bullet at 3400 fps), .257 Weatherby Magnum (115-120 grain bullet at 3300-3400 fps), 6.5x68S (120 grain bullet at 3300 fps), .264 Winchester Magnum (120 grain bullet at 3300 fps), .270 Weatherby Magnum (130-140 grain bullets at 3300-3375 fps), 7mm Weatherby Magnum (140-150 grain bullets at 3300 fps), 7mm STW (140 grain bullet at 3325 fps), 7mm Ultra Magnum (140 grain bullet at 3425 fps), .300 WSM and .300 Winchester Magnum (150 grain bullets at 3300 fps), .300 Weatherby Magnum (165 grain bullet at 3350 fps), .300 Remington Ultra Magnum (165 grain bullet at 3350 fps), .30-378 Weatherby Magnum (180 grain bullet at 3450 fps), and 8mm Remington Magnum (150 grain bullet at 3400 fps). As you can see, all of these cartridges launch general purpose hunting weight bullets (for their respective calibers) at 3300-3450 fps.
If you check the Rifle Trajectory Table you will find that the typical trajectory of these ultra-long range magnum cartridges allows a scoped rifle to be zeroed to hit about 2.3" high at 100 yards. From a rifle so zeroed the bullet will hit approximately 3" high at 150 yards, 2.6" high at 200 yards, and about 3" low at 320-330 yards. By going to a big magnum cartridge, and suffering the added recoil, muzzle blast, and expense that entails we have only gained an average of about 20 yards (6.6%) in MPBR over the standard .270 Winchester.
The most over-the-top cartridges among these, using the lightest bullets in their caliber suitable for even the smallest big game animals, can gain a few more yards, but at the cost of their versatility for use on larger game. For instance, the .300 Ultra Magnum with a 150 grain bullet at a MV of 3450 fps has a maximum point blank range (MPBR) of 335 yards. The .257 Weatherby Magnum with a 100 grain bullet at a MV of 3600 fps has a MPBR of 337 yards. The .30-378 Weatherby Magnum with a 165 grain bullet has a MPBR of 342 yards. The .300 Weatherby Magnum with a 150 grain bullet at a MV of 3540 fps has a MPBR of 343 yards.
These are radical, over-bore cartridges shooting the lightest practical bullets, and they average a MPBR of 339.25 yards. This represents an average increase in MPBR of less than 15 yards (4.6%) over the same cartridges shooting heavier bullets of far greater all-around usefulness. By almost any standard that is a poor trade-off.
He closes with:
It is singularly amazing how relatively little practical hunting range is gained by using an ultra-long range rifle and cartridge (compared to a standard long range rifle and cartridge). To pick up (at best) 38 additional yards of maximum point blank range, a deer hunter has to move from a reasonably handy, medium weight, versatile rifle to a long, heavy, specialized rifle with a huge increase in recoil, muzzle blast, and expense!