well... im trying to develop the simplest to play build going on, and ss would probably be better than backstab, assuming you have a nice slow mh weapon. and as far as energy efficiency. also for mut you want the fastest daggers you can find. 1.8 speed isn't what your shooting for any longer.
stask... as far as what spec you play, as long as its not retarded, and does an appropriate amount of dmg for your gear, its about what you like to play, and what you have fun doing. if the weapons/gearing exist for you to run combat swords or combat daggers, be my guest.
hemo is still something im looking at, sub has its finer points. i've got a semi broken combat daggers spec going on, with an emphasis on envenom. the current gear level, envenom scaling may not be worth it, but thats based on ap, so if your ap is high enough, envenom should do tremendous amount of dmg. (somewhere around 4k unbuffed).
unless there is some other scaling issue im missing. raid or rogue wise.
a very ugly backstab build. -note, i don't play rogue