I agree, the slower your swingtime is, the better you can perform sealtwisting without screwing up your other CDs.
I've tried sealtwisting on Brutallus and during the bloodlust + hastepot time i totally messed it (analysing the wws, there were some swings even without any seal).
The burst potential of sealtwisting also should be considered. If you get a WF+SoC proc, there will be 3 SoB procs after it :
19:29'32.546 Carpathia gains 1 Attack from Windfury Attack
19:29'32.546 Carpathia's Swing hits Brutallus for 1630 Physical damage
19:29'32.861 Carpathia gains Windfury Attack
19:29'32.889 Carpathia's Seal of Command hits Brutallus for 1673 Holy damage
19:29'32.889 Carpathia's Swing crits Brutallus for 3822 Physical damage
19:29'33.283 Carpathia gains Seal of Blood
19:29'33.690 Carpathia's Seal of Blood hits Brutallus for 900 Holy damage
19:29'33.700 Carpathia's Seal of Blood crits Brutallus for 1809 Holy damage
19:29'34.129 Carpathia's Seal of Blood crits Brutallus for 1838 Holy damage
so be careful on high threat situations
If you want to give sealtwisting a try, it's essential to use an accurate swingtimer mod like
Doc's Swingerclub and practice the above-mentioned rotation