Suffering was only adding a stack (or a chance to add) on the application of Rupture, not for each Rupture tick on the PTR last time I tested.
Using more Ruptures would theoretically increase the number of procs per minute, but that would be so inconsequential it would be meaningless.
EDIT: Has anyone been on the PTR to test the proc rate of Suffering lately? I did some 10 minute tests of that and the Mutilate cycle question.
The proc rates I got for Sub and Mut were very different than what I remember them being several patches ago, I had 35.9% as Sub, 30.9% as Mut, and 13.2% as Combat.
I also checked out the SS as Mut topic and it was a little bit of a let down. I used a 1+R/5E rotation (possibly not ideal), combat reforging for both, and
this spec with SS being the sole CP builder. It was about 15% behind normal spec and rotation. Both tests were done over a 10 minute session on the dummy.
There's a lot of room for error in that, but 15% seems like it's too big of a deficit to be made up.