Many like the 84mm, but personally I think there is to much resonance in the cabin.
It would be best to catch a ride with a fellow Pelican who has the 84mm setup to get an impression.
Hard to evaluate in a video but I think this German guy has the SSI/70mm setup:
https://www.youtube.com/watch?
My SSI's with 2-1 70mm dansk sports muffler:
