Asn + RS is what you need.
Being able to maintain +15% crit (+5 more with the asn tree) almost 100% of the time in the mid-20s range is key.
You can do a LOT of damage with rs-asn as a leveling spec, plus you get heal-on-kill and rift barrier from rs for larger and longer fights.
RS may be half of the main rogue tanking spec, but it has insane damage output when you pair it with asn's crit based stuff.
Always check for black-on-black text.