This is what your (and by the looks of it, mine too) rotation is gonna be, so far.
0.0: Rend
1.5: MS
3.0: OP
4.5: Empty, Slam or SD proc
6.0: Empty, Slam or SD proc
7.5: MS
9.0: OP
10.5: Empty, Slam or SD proc
12.0: Empty, Slam or SD proc
13.5: MS
15.0: OP
16.5: Empty, Slam or SD proc
18.0: Empty, Slam or SD proc
19.5: MS
21.0: OP, Rend falls off
And then it all starts again. That's pretty basic, but that's what it's going to be, unless they decide to drastically change something.
Bladestorm would probably be best used either right after Rend falls of or before you use Rend.
Like probably, you'd do something like this:
0-21.0: Rotation above
22.5-28.5: Bladestorm
30.0-51.0: Rotation
52.5-73.5: Rotation
75.0-96.0: Rotation
97.5-118.5: Rotation
120.0-126.0: Bladestorm
And then repeat as necessary.
Of course, this all depends on a stationary fight or one with limited movement and no gimmicks/adds/whatever.