Water buff, not sure I would recommend the Accubond. This is one of those cases that me personally would give up some long range ballistic performance for better close range terminal performance.
Penetration is key with these big critters so if the bullet does not get through the vitals, we have trouble on our hands. Personally, I would look hard at the 285 gr TSX or the 280 gr LRX for this use. The 275 gr Swift A-Frame would also be a great choice. Again, our main goal is penetration above all else, break down the critter at the same time you drive a bullet through the vitals so I would really have to go with a heavy barnes or a Swift A-Frame and again, live with the fact that your giving up some range for better penetration and close range terminal performance.
I am personally not a huge fan of long range dangerous game hunting. Now I am not one to demand that you need to get within 50 yards to place your shot. There is no reason that a well place shot can not be made out to 300-400 yards, but 1/2 mile shots on dangerous game can result in some serious problems.
My personal opinion would be to step up in caliber to be honest. The 338 is a great chambering and it will certainly do anything you need but the 375 cal would give you a more authoritative impact on heavy game. I just tested the 350 gr TSX in my 375 AX and at 1000 yards, it shot extremely well and its a VERY long, heavy bullet for the 375 cal. I would recommend at least a 375 RUM to drive this bullet weight or larger.
The 300 gr Swift A-Frame would also be a great buff hammer.