My rifle likes the 300 SMK best of all that I have tried.
A MV of 2730 or so is only ~100 FPS off of the 338 Edge MV with the same bullet says the velocity is good enough for any thing I go after and at pretty much any reasonable distance up to 950 yds limited only by the capabilities of the scope.
In May 09 I went to South Africa and shot 13 plains game animals with my .338 RUM and 250 Swift A-Frames. I have to say that I was most impressed with the bullet performance. I shot a lot of heavy bodied animals like a Wildebeest, Kudu, Zebra and Gemsbok. The only bullet I recovered was from a Wildebeest and and after traveling most of the length of the animal, still weighed 237grs. I have also taken two large black bears in British Columbia the year before while on a Griz hunt and they preformed equally well there. I only wish I could give you a report of how they did on a Griz, but it was not to be.
I don't understand what you mean that the Barnes are not performing. They are the only perfectly forming 100% dependable hunting bullet on the market that shoots like a target bullet with an acceptable BC. The BC is not quite at the top of the heap, but close, and in hunting BC is only one of the factors to consider. Hunting is not target shooting. I have shot or guided hunters who have shot animals with virtually every bullet you listed. You said grizzly so eliminate most of those. Yesterday four of us were shooting some 338-300 ultramags that I built back in 98-99 time frame using the 225 Barnes TTSX. These have had quite a few shots through them. We were holding 1" groups out to 400 yards with them at velocities up to 3320 fps with low extreme spreads. The new Barnes with the cute little rings cut in them will shoot like a target bullet.
I honestly thought and hoped the 225 Accubond would be the answer but it has failed miserably out of several big 338's this season at various yardage out to 750 yards. Just blows all to crap when it hits something. The Barnes blows right through anything with a perfect mushroom every time. It is the premier hunting bullet on the market.
With your 338 ultramag you have a very good half mile rifle and most hunting is done inside that range. With the 300 matchking you can go beyond that but I like a bigger 378 case or something going that far. You mentioned grizzly, no 300 matchking. I shoot a lot of bullets and test a lot of stuff through all my contacts. With all things considered in a bullet to take everything in North America with a 338 ultramag I am convinced the 225 Barnes TTSX at .514 BC is the best hunting bullet available. BC is actually a little better than that I think. The next would be the Swift Scirroco 200 grain at .507 BC. The Swift is tougher than the accubond but still nothing beats the Barnes for performance on game so I list it number one. The BC on the Swift would be max. It might be slightly lower but very close to that.
With the 338-300 and the 338 ultramag I think they are best suited shooting the lighter bullets giving you a much better trajectory eliminating click adjustments out to 800 or so yards. Just use a mil dot scope and get on game quick. I would not have killed my big bull the other day with my 338 ultramag at 740 yards if I had to use clicks. Just didn't have time. If I am shooting the 300 matchking way out there I shoot a bigger gun that gets substantialy more velocity than the ultramag stuff.
Predictions are difficult, especially when they involve the future