This is my 6 piece sentry set I use for Legendary diff missions and incursions. I have the Devil/Heel combo running and have them setup specifically for quick accurate repeat shots. The damage increase from the set more then makes up for loosing out on a few weapon mods worth of headshot damage. The ammo box is used after abusing the weapon swap setup of the two guns, giving you a 66 round sniper rifle before you have to reload. The small RDS scope works a treat on PC not only for the added stability, but also if you "scope in" with it, you just get a slightly closer over the shoulder view, but your crosshair movement is drastically reduce and smoothed out. Once you get the timing down on when to fire with the crosshair settling down, you can nail headshots with quite a bit of speed and quite a bit more damage than an MDR.
Granted its not as fast as making stacks as the MDR, but with a tiny bit of patience its like having an MDR and a M700 rolled together on the 1 weapon set. Works a treat at dropping Elites and bosses in the hardest content due to the immense headshot damage that can be generated by the set once 6 marks are on targets.