Discharge is used on CD regardless of pvp/pve..simulationcraft has proved it.
If you are talking about the sithwarrior.com forum. They have even stated in the thread that it's best to wait for 5 stacks, but the dps loss is ~1percent DPS. Please don't state things that are random tosses of misinformation spouted by the misreading of a thread.
I stated in pvp is the only time not waiting on 5 stacks is not a dps loss. This is inherently true a loss of 1 percent is still a loss. If you feel you can't use discharge when it hits 5 without waiting a few GCD's to pop it than use it on CD between 3 and 5. Using Discharge with less than 3 stacks on it is a significant dps loss.