What has been your experience with the Norma Oryx Bullets 375 Caliber 300 Grain Protected Point? Are they good for Cape Buffalo? If not, maybe for the largest plains game.

Norma Oryx bullets are too soft for buffalo. I have no experience with them on buffalo, but have seen plenty of them on PG and lions, in calibers .270WSM, 280 Rem, 7x57, 30-06, 358 Norma Mag, 9.3x62 and .375.
They fail to shoot through most animasl, from warthog up to kudu, because they open up too big, and although they retain a high % of weight (normally), they do not penetarte well. In calibers 9.3x62 and .375 (286 and 300gr respectively), they did not shoot through at least 3 lions, if I remember correctly. One shot was angled from behind, (9.3), and although it killed the 190kg lion male after getting into one lung, the penetration did not impress me. Another (.375) did not shoot through a problem female, broadside at about 70 yards, and onother did not go through a male, lying broadside under a bush, at about 20 yards. (In the last case, the bullet did hit the spine though).
So IMO you should look at Swift A-Frames or Barnes TSX bullets for your buffalo hunt.

I like the Oryx for lion from my 9,3. Always gets through the muscles and opens fully. No over penetration to would others in the pride, and max stopping power...On buff??? Have killed one with a frontal chest shot that went under the chin and broke the spine. One is not enough to base on and at higher velocities (as from your .375 as oposed to my 9,3x62) they are going to open too much - like the standard woodleigh softs. You have a choice of well proven bullets- leave the experimenting to others. From a .375 The TSX gets my vote