To compare the two passives, I put together a DPS model that simulates a 180s fight on a single, elite target using the standard M6 cold build.
I modeled the numbers using my DH in particular, and assumed a CD time of 5s on sentry drops (due to CDR).
Additional assumptions would include: target being in sentry range 100% of the time, 100% sentry uptime, highest possible uptime on wolf companion activations, etc, etc (basically perfect conditions).
The results are as follows:
Ramp Up Period [0-20s]
This is the stretch of time when sentries are deployed in 5s intervals, the first being dropped at 0s.
As expected, Steady Aim comes out ahead with a 16% damage bonus over Custom Engineering. Resulting (in my particular case), a damage differential of a little over 500 million by 20s.
Steady State [15 or 20-180s]
The period of time from the last sentry drop to the end of the engagement.
After the fifth turret is dropped (@20s), Steady Aim's lead over Custom Engineering slowly diminishes at a linear rate, until it hits the break point at 40s. From 40s onward, Custom Engineering has a DPS advantage over Steady Aim.
- At 60s, Custom Engineering has a 3.0% damage advantage over Steady Shot.
- At 120s, Custom Engineering has a 5.5% damage advantage over Steady Shot.
- At 180s, Custom Engineering has a 6.2% damage advantage over Steady Shot.
In Grifts, I find it very difficult to have all five sentries up at one time, within range of my intended target. So I prefer to use Steady Aim due to the quicker ramp up, for faster clearing of trash mobs and elite packs.
Rift Guardian fights, and high density areas with abundant choke points is where Custom Engineering really shines.
In the end, I think that the numbers are so close that it really all just comes down to personal preference.
Here's some more tables,
Note: "By skills" includes Cull of the Weak (20%), Steady Aim (20%), and Wolf Companion (weighted value based on uptime, 8.75%)
Sentry DPS table w/ Steady Aim:
Sentry DPS table w/ Custom Engineering: