To answer some questions about weapon swapping, I used simulation to estimate the dps value of swapping for mutilate and combat, as a function of time left on DP before the swap. I used ilvl245 gear as my base since it's closer to the gear most raiders are currently wearing. However, I used talent and gem settings that are optimal for BiS items since I did not have time to check what would change for ilvl 245 items, but I do not think it would affect the shape of the graphs much.
Mutilate: 51/18/2 spec, double mongoose, AP gems, CT+DC, envenom-only cycle.
Download MuteSwap_liter.bmp
Combat: 51/18/2 spec, double mongoose, AP gems, CT+DC, evisc+rupture cycle.
Download CombatSwap_liter.bmp
Note that I am using AP gems instead of soft armor pen cap setup for combat. I found out that for weapon swapping, the highest dps is achieved with that setup. The agility setup is about 50 dps behind, and soft armor pen cap setup is another 50 below.
As far as optimal switching time goes, it's somewhere between 3 and 4 for both spec, slightly closer to 4 for combat and slightly closer to 3 for mutilate. The benefit of swapping is higher for mutilate as expected by slightly more than 100 dps.
EDIT: If you want to see the graphs that show the DPS value as a function of swap time for mutilate and combat, follow the links. Embedding the graphs in the post was a mistake since they have too big of a size and people decide to quote the message.