Just want to summarize what has been posted and what I have found for 44/27 and 32/39 builds
Generally these 2 specs will out do unholy builds most of the time even with DW users having less gear.
fast/fast is usually better as it can simply proc more KM.
I don't see how using slow/fast to boost PS/BS and FS is worth the extra KM procs fast/fast provides, after the first rotation its just IT spam and a single PS renew DC dumps etc and read below for FS.
Only use FS when you have a KM proc AND HB/IT are on cooldown as this allows for another KM proc before the next HB is up OR when there is simply no KM. Otherwise IT for KM procs (only when HB has just been on cooldown) and DC for RP dump.
During a trash aoe pull your HB should be at 100% crit rate, KM should always be up before your next HB. Even for single target fights it should be close to 100%
It is good to prioritize HB on the first rotation and use BB and RP dumps to wait a bit for a KM proc and when it has around 2-3sec left on cooldown and KM is up, don't waste it on a IT or FS.
So basically if KM is up you should ONLY use it on HB UNLESS HB has just been on cooldown AND IT is ALSO on cooldown and in this case use FS.
You WILL be taking aggro if your tank is bad and/or undergeared after a PS>IT>PEST>KM'd HB. So use BB once or twice before HB to let tank get some aggro.
During heroic boss fights where you know the ghoul and garg will stay alive it is not hard to pull 3-3.2k dps with rep swords and some heroics gear.
Wyrmrest rep swords are great for starters and will allow for everything I noted above, you won't need to upgrade till naxx.
You should be using FC and Cinder/Razor for the other weapon, whatever suits you I personally use cinder for the extra HB and IT boost and Cinder seems to proc a lot.