I'm thinking that there won't be a huge difference between the best weapon in the game vs the worst weapon in the game, in terms of strict DPS. Bungie has already said that kill times in Destiny are much shorter than Halo. You wouldn't be able to say that unless a) your encounters are scaled based on your weapon's potential, or b) there isn't a wide range. I'm thinking the difference between the weapons will be 1 or 2 shots to kill for slower firing weapons, 3 or 4 shots to kill for mid range weapons, and maybe 5 or 6 for your fastest weapons. The incentive to go back out into the world for better loot is not in your damage dealing potential, but in the other behaviors of the weapons. (Closing time cloaks the user while ADS)