I have never heard that the critical divisor in armor makes a difference in maneuvers.
I've been fucked up just as hard in plate as I have in robes.
Channeling 302 really isn't worth it, too much risk for maybe 10-15 extra damage.
In the rift, I one hand open guarded channel 317 and especially with 240 up I just wtfpwn everything, although I am in COL and have to hit the reserve tanks frequently.
In 4x torso chain and 4x runestaff the only thing that kills me is tangleweed.