The .375 JDJ w/the right load is a proven killer, that is no doubt.
But I think you are on the right track w/your .30-06...........
Provided you use a good premium bullet like the 2 you spoke of, Barnes triple shock "X" 180 grn or the 200 grn Swift A-frame.
You have said this is a gun / barrel combination that you are comfortable with, being comfortable & confident w/your firearm usually means you will put the bullet where it needs to go. Work up a powerful load w/one of the premium bullets you mention for your .30-06, put that bullet where it needs to go on that first shot, and you will have a successful hunt!!
As a side note, I would contact the guide to let him know well in advance of your trip, what you intend to bring as your firearm & load of choice. Most guides have a "minimum" that they will take a client out with. I know an old timer here in Alaska that hunted & killed his moose every year for 30 years w/a .243 winchester. When I went wild boar hunting in California, the guide stated they will NOT take clients out w/.243 riles or .357 handguns, you have to have something bigger then that or they will loan you something of acceptable caliber.