The .408 was designed specifically as a long range round, much like the .338 was. 50bmg has been "turned into" a long range round because it was the biggest and baddest at the time, but the components to really make it shine have been developed by shooters as the sport has evolved.
The .408 was created in an effort to present a packaged long range round from day one. It is "supposed" to have better ballistics than the 50bmg, but I think that is probably better than the "stock" 50mbg ball round. I don't know how it would compare against a good VLD 50bmg load.