Hey guys, thanks for the input!
I think I'll get Scabbard then, as rep costs yesterday were about 15k as well
My best try I got him down to 15% after having transitioned with 1m 05s remaining. This even was with food (feast - so darn mastery), flask, pre-pot, pot, Augment Rune and Drums of Fury and having prolonged BoS for quite a long time. Also I'll be in the market for some multistrike food.
For some tries I managed to team up with a lock for the multistrike buff which seemed to help a lot, but I only had tries with 40ish seconds left which only gets me to ~45% (I don't waste drums then).
Bottom line: I too think my mastery stacking is killing me here.