FD was last updated on 8/26 and is working off an earlier build. SimC was simming about 10k dps higher than FD for 17331 (the build that FD is using, I believe). SimC is now updated to build 17345, and Lokrick claims it is now more in line with BM mechanics on the PTR.
Also, SimC has always been more accurate at modeling haste than FD. Zeherah has certainly acknowledged that. I know that for both simulators, they are not accurately modeling MM rotations (Lokrick detailed his attempts at addressing this
here), but I'm not entirely sure about the limitations of the BM profiles. We'll certainly see updates to the simulators in the next 3-4 weeks as Lokrick and Zeherah have more time to adjust to the 5.4 changes.
Edit: P.S. I am still recommending BS over AMoC on the BM guide. Such a small gain is negligible when considering in-game mechanics, the focus requirements of AMoC (especially given the increased focus cost of AS), etc. Besides, simulators tend to award more hits from pet-like abilities like crows and DB than what actually occur in average parses. We could be seeing something like that in SimC right now for AMoC.