The crit chance from the Crit+ skill might stack additively. With Crit+ lvl 5 giving a 25% chance, stacking 4 of them might just give an overall 50% damage boost.
Did some not-so-scientific testing with Wheeljack vs the first Devastator fight, Commander difficulty, using two Burn Sniper Rifles with similar stats.
Weapon 1, 3277 damage, consistently killed Devastator 10 times in 21 shots.
21 shots = 68817
Weapon 2, 3261 damage, 4x Crit+ Lvl 5, consistently killed Devastator 10 times in 14 shots.
Assuming the Crit+ chances are independent, 4x Crit+ Lvl 5 should be around a 68% chance to crit. With 14 shots, thats an average of 9-10 shots that deal 1.5x damage
9 shots crit, 5 normal damage = 60328.5
10 shots crit, 4 normal damage = 61959
So with an expected crit distribution, I shouldn't be killing Devastator 10 times consistently with only 14 shots.
Instead, having a 100% crit chance with 14 shots is 68481 damage which is a lot closer to Weapon 1's output.