So I won't even argue the math on which does more damage, I think its been pretty clearly proven that combat swords is the more efficient leveling spec. HOWEVER, I love Muti. Just like the OP I leveled most of the way on combat swords but it just didn't feel roguish...
I switched to muti at 62 but frankly it was tough and probably a little too early. Switched back to muti again at 66 and I love it. Way fun, and I feel like a rogue. Sneak around, CS, muti, KS, etc.
Of course it is a pain in the *** when you get a few adds, no more AR, BF. But then I'm a rogue, I should be standing toe-to-toe with 3 ogres....vanish and try again.
So anyway, try it, you might like it. Have fun and don't worry if you have 5.6758 less DPS than you could have
and to answer your question you get behind the target with Stealth, CS and KS. Gouge does break from poison, sometimes you can time it right but certainly not reliably.
Also make sure you turn with your mouse! Keyboard turning does not work with muti....see the post on that...