Max temp-stable load for the 175gr in 7mm WSM is slightly over 3000 ft/s out of a 24" pressure constrained to 63 KPSI (Retumbo). It's 2980 ft/s for a RM (Retumbo again), and the difference is due almost entirely to a reduced max pressure at 61 KPSI. That max pressure reduction is artificial with modern rifles, and at the same pressure as the WSM the RM gets very similar results with case capacity being about 1gr H20 more in the RM and the WSM shoulder being slightly more efficient.
So now we understand part of your confusion - you have inaccurate data. That's not totally your fault as the 7mm RM and WSM data is unusually bad even compared to the general disaster that is published reloading data.
The Weatherby is 5grH20 bigger than the RM and 6gr bigger than the WSM. But it hits a bad spot in terms of powder availability and gives what advantage it had back, hitting in the low 3000s with the 175gr and Retumbo as well. What it really wants is "slow Retumbo" but no such powder exists. A couple of non-pressure tested loads have been published as high as 3070 ft/s, but that's a LONG LONG ways from the 150-200 ft/s you claimed from the throat.
In fact, the idea that you could get a "free" 150-200 ft/s just by changing the throat is laughable. Not only does it defy everything we know of interior ballistics, but if it were possible we'd see long throat versions of every cartridge as no one would be able to pass up that free lunch. In reality, everyone has tested it, and it doesn't provide any benefit. When you lengthen the throat, both pressure and velocity go down. When you add powder to get back to MAP pressure, you end up back very close to where you were velocity-wise. With some powders, you gain a few ft/s. With some you lose a few. With Retumbo (which is the fastest temp-stable option here) you actually lose a bit.
