This seems right to me. Since it's back-loaded with setup, it really would be best on bosses and such that live long enough for you to get the full build-up and BLAM! Or in pvp where you'd use it to set up burst and tear something apart. While questing, I would think Mortal Combo would probably be better for ripping through things. Or In for the Kill if you want to use MS more than Execute, but not sure how often you really get to utilize it on quest mobs. You could probably just spec MC for the double tap of MS, then if you find a rare mob with more health or something, just easily swap to FR... oh wait...