Reaper Set Swaps
The most important swap for reaper is the compelling set for claw swipe. It allows you to spam a soul gathering skill, and is extremely important for your attacks per second.
The next swap that is nice to use is either 3 piece ln 100 set or 4 piece 110 black out set for master's scheme cooldown. It allows for an extra 7 soul without needing to gather the souls every 20 seconds or so
Then, there is the 2 piece oc/sc swap, allowing for a massive claw lunge hit, adding 60% damage to it.
The final set swap is 2 piece grief/celestial sets, which gives 60% cooldown reduction to backstab. that makes it a 3 soul gathering skill every 7 seconds.