Okay, I've scouted around for an answer to this. Elitist Jerks don't really mention the drawbacks of dropping Rupture, and ShadowCraft tells me I'd lose less than 1k dps.
Is it worth keeping Rupture up? I did a test on the Dummy and I got a significant *decrease* when I DID use Rupture, but I don't know if that's just because I'm out of practice with it. It seemed like so much effort to keep SnD and Rupture up, AND try to Evisc in between.
Or shall I drop Combat altogether and roll Assassination? :P