If I remember correctly, and I haven't played combat since end of Cata, if you're using AR with with Bloodlust then you're energy capping and essentially wasting resources. This is presuming you're playing Combat of course.
I have yet to fet my 4th T15 piece but I think Combat is the best way to go from what I have been reading. Something about Shadow Blades and AR being pretty good together every 1-1.5 minutes or something.
Then to answer your question no. I also play assassination with ilvl 525 (about half haste/half mastery), Without bloodlust I wait till i'm almost full energy and then begin the mut, mut, envenom...
With BL you can pretty much start anywhere and do the same thing. I believe the GCD becomes 0.7s when shadow blades is acivated as well.