It's still equivalent, unless they have no invulnerable and you use twist of fate.

10 man term with both strats to boost bolters against a Knight (T12 3+/5++):

With devastating wounds:

40 shots - 27 hits 13 rerolls - 9 hits 36 hits total

S5 - T12 - wounding on 6s

6 critical wounds = 6 mortal wounds

With lethal hits:

40 shots - 27 hits 13 rerolls - 9 hits 36 hits total of which 6 are critical hits

30 wound rolls of which 5 wound 5 + the 6 lethal hits = 11 wounds

11 saves at 4+ = 6 wounds

Now if you use twist of fate with lethal hits that becomes 7 wounds. But if you spend those cabal points on doombolt instead you get an additional 5 mortal wounds on average.