Yeah I do like 1kish+ (varies wildly depending on party make-up) if I never, ever drop deliv the entire fight (this can make you unpopular :>). 870 sounds pretty solid for MTing the first phase of that fight. A lot of those sick Sephi parses come down to gear, time-to-kill (TTK) and party combination (AST babysitting you says hi). For instance one of my best parses was when I was in a group where I was the second highest DPS. The low DPS allowed me to fit in a 3rd berserk at the start of the add phase and not lose it for the opener in P3 it also had a NIN and a MCH, I was only short an AST for world's luckiest WAR.
Regardless, I can see your problem just looking at lodestone. It starts with a W ends with an N (also haven't melded some pieces). Seriously 1050 with your gear is about right. A Weapon will add 50+ to your dummy parses alone, which brings you within striking distance of me and my sub-optimal gear. We're on the same server, hit me up if you want to chat.
I struggled with this problem as well when I switched to WAR not long ago. After some experimentation (and deep loathing towards A8S dummy) I found that if I weave in fracture twice (preferably at 4+ Wrath stacks) + infuriate Fell Cleave as soon as it's off CD, at my current SS it means Berserk is up on my heavy swing after the fourth stack. That means I can go ape the moment it goes off CD. Once my skill speed gets high enough, I'll probably alter my rotation to drop fracture and fit in an extra Fell Cleave. Mainly because I'm lazy and fracture is a button I really ceebs pressing.
Given the options you presented, I'd just sac the two stacks to the wind. Holding Berserk will give you a terminal disease (unless you only get one more Berserk until the boss dies, then ya it's ok). EDIT: I think I was wrong here.
