I'll post my supporting arguments and would hope you do the same.
300 WSM v 300 WM - the 300 WM needs more powder to get the same pressure/velocity because it is a bigger case. When run at like pressures with optimal powders the WM outruns the WSM. Have had and loaded for several examples of both.
Ex/ 180 gr boolits: Nosler WSM 3082, WM 3160; Sierra WSM 3000, WM 3100; Hodgdon WSM 2991, WM 3042
I have a bit of experience with the 375 but have only owned 1 - although this isn't about experience with ABC cartridge. Its about reloading acumen and knowing what is happening inside the case when the primer ignites the powder. The Ideal Gas law is as close as I know of explaining what happens inside the case. The simple answer is that bigger cases win the velocity race when like geometry and conditions are used.
For the 9.3 using a 286 and 375 using a 300:
Nosler 9.3, 2414; 375, 2600
Hodgdon 9.3, 2407; 375 2645
More case capcity means more velocity.
I'll assume Nosler used SAAMI/CIP pressure specs to arrive at their data (375 - 62.0k psi)(9.3 - 57.0k psi). I will note that the Hodgdon was run at 46.3 CUP for the 9.3, 49.5 CUP for the 375. Even though the 9.3 could be gased a bit more, it isn't going to overcome the 200+ ft/sec between them.
Powder ignition isn't linear but a close approximation is 1 gr of powder equals 2500 psi and 35-40 ft/sec derived from 180 gr bullets from a 30-06 using pressure tested data and 6 powders. I would not use that relationship when working at top end loads - in general pressure rises faster than the linear relationship suggests at 63-70k psi.
Re 17 - I've used a good bit of Re 17. I believe it to be faster than either 4350. I can make my WSM's run faster using Re17 but not by 100 ft/sec. It is a good powder and does add a bit as Alliant's own website indicates - even though they used some rather generic velocities for the cartridge/bullet combos. In fact, I can pick alot of non Re17 powders to reach and exceed the vels quoted in the Re 17 literature. It ain't magic.
