Norther: Dual Crusader does not 'stack' but it does increase uptime significantly. According to my math
here, even unbuffed and with suboptimal gear, Crusader OH handily beats berserking OH in raw attack power contribution. Add in the fact that Crusader gives strength which applies to Ghoul and multiplies with Kings, and add in the fact that it does very nice things double-stacked with DM:G, and berserking really looks rather odd. The only potential benefit Berserking has is that you can theoretically double-stack it with Crusader for Gargoyle, but really, at 1.2 PPM that isn't going to be near reliable enough to make up for the huge loss in power.
The logic behind Razorice/Cinderglacier being better than Berserking is simple: they are considered superior to FCx2, and FCx2 is superior to Berserking. Whether they actually
are superior to FCx2 isn't entirely clear to me; the scaling factors are murky but I definitely can see FCx2 pulling ahead at very high strength levels.
Also, if your melee is 1/3 of your damage, you're obviously counting Necrosis. I'm pretty sure Cinderglacier does, in fact, affect Necrosis (and any other periodic/proc shadow/frost damage) without using a charge.