What sword were you using before you picked up malch? Combat swords does do more DPS than 41/20 mute on average. There are some fights where mute can definitely hold it's own and even give you advantages - typically stuff with a lot of run in/out stuff where you come in with full energy (prince depending on who he shadows, gruul, etc..). I leveled as sub mute than went combat at 70, playing that up until we hit hydross (a lot of kara, gruul, and mag). I've also used it on most of the boss fights in SSC just because I was PvPing with it and didn't feel the need to respec for farm bosses. 41/20 can truly put out great damage if you have the gear for it (two good daggers), and pay attention to your finisher cycle. 2 piece T4 definitely helps too... as those 3 extra seconds of SnD come in very handy at times. I switched to combat daggers (a build I had played extensively at 60) and was rather disapointed at the lack of a DPS increase over mute. The change to swords yielded a decent DPS increase... but combat daggers was on par with mute in my experience. I was using S1 shanker + malch for 41/20, S1 shanker/shiv set for c-daggers, and then I bought a S2 slicer the first day S2 came out and didn't look back. When I get back into raiding and well just overall playing again I'm going to check out mute again. To my knowledge there are no dagger rogues in our raiding core right now, so I could probably grab the dagger from vashj when it drops pretty easily... We can easily kill VR + hydross with a DPS or two missing anyway... so I don't have to worry about that being a problem either... sounds like it might be time to go back to mute!
Sorry for that one large paragraph haha... I'm a bit burnt out from all the exams last week... I no longer do paragraph form!