I killed a big Scimitar Horned oryx with an 85gr Barnes xbt going 2900fps from a little long barreled 6x47 ( 222 Magnum necked up to 6mm) I had just had a neck fusion. Base of the neck at 184yds, complete penetration. A 243 can push it a tad faster!
I have not killed an Oryx but this doesn't surprised me. Did you recover the bullet?- maybe not
