I'm also playing currently Subtlety and I think going max Crit with Grievous gear will be good idea.
Right now I'm feeling kinda weak, though we have "many tools", I'm feeling that they're useless vs warrior damage.
Not sure about Assassination, haven't tried it yet. But many people are talking it's great spec, I'm pretty sure I'll check it on the arenas.
I've heard multiple high-ranked streamers suggest that Assassination right now, then Sub when your gear is "current"... Not sure exactly what evidence they have to support it, just echoing their thoughts.