I'm not sure it's something that can be easily modeled for calculating dps differences. Sure, we can and should still use femaledwarf.com to work on "what's better", but we may need to put in some assumptions and take things with a bit more salt.
The crazy part of having T13x2 is that as a MM hunter doing hard-cast AiS, you sometimes do shot fragments like this:
CS -> AiS -> SS -> SS -> AiS -> AiS -> SS -> CS -> SS -> SS -> AiS -> AiS -> SS -> SS -> [repeat]MM rarely if ever did anything like that because focus wasn't available to do much of any value except another SS. And you really wanted to do that second SS to keep the improved steady shot up.
Well so in walks the 4pc T13 and the proc is very very good. I find I am compelled to get the T13x4 to proc. Again, I play MM and previous to 4pc would do a great deal of hard-cast AiS -- basically any time except when on the move or on trash that would die too soon. But now I'm doing different even more weird shot fragments like:
CS -> AS -> AS -> SS -> SS -> AS -> AS -> AS -> AS -> SS -> SS -> [repeat]until I get a proc and then I switch into hard-cast AiS.
While I list "rotations" or "priorities", the coming of T13 turns all of that on its head. MM has many priorities. Keep the sting up, use chimera, maintaining ISS, and getting that T13x4 proc. When you add in movement and game mechanics, it really can't be called anything other than nuts.
One essential item for all hunters is having a very visible hunter focus bar front and center. If you don't have one you need to get one. Here are a few that do it for you (in my order of preference):