I ride 2-up for snowboarding quite a bit. I have a 155 Pro but rode a 163 M8 back to back on the same terrain, same conditions this weekend. I was so surprised at how similar they turned. Both sleds will turn on a dime. I wouldn't hesitate to go with a 160+ track in the future for the extra flotation. That said, I can climb, side-hill, boondock, make downhill turns, etc on my 155 Pro with the wifey on it with me, no issue. We don't tend to climb steep/deep 2-up if it's sketchy/committing. We almost always do those climbs with 1 rider then come back and grab the second after the track is in place. So much of riding 2-up to challenging terrain is about the rider and passenger being dialed.
Bottom line - both will get the job done but you might have a slightly easier time with the 163. Neither will be a substitute for getting your 2-up riding dialed.
EDIT - Saw you were concerned about jumping. I have very little time on the 160+ tracks but the consensus is you give up a bit of jumping performance. Not that they can't jump, just not as proficient as the 155. I guess it depends on how much emphasis you want to place on jumping.