I feel that just because Sasuke beat Orochimaru doesn't mean he can beat anyone that Orochimaru was stronger than. Case in point, I haven't seen anything yet that indicates the current Sasuke could have pushed The Third into using the Reaper Death Seal (I don't remember the real name so the Toonami one will have to suffice) and thus killing him.

I think that Sasuke's Sharingan is a lot of what's giving him the upperhand in fighting. He knows what's going to happen before it happens and can see through techniques, that give him a massive advantage over most people.

That being said, I doubt that Suigetsu is a threat to Sasuke since he probably wouldn't have recruited him without sufficient confidence that he could either control him, or beat him if he stepped out of line.