I finally had a good day winging with the 870. Rode in bay chop so nothing too big. About foot and half wind driven bay chop/swell. Rode the first hour with the 140 and a blue shim. Then the second hour with the 130 surf and blue shim. What a difference. With the 140, that thing would glide like it had a motor. But the turning to me felt stiff. I felt awkward. Made me question the 870 a little bit. Then when I put the 130 surf tail on, it made it a lot more agile and friendly. I could turn at will. Still had very good glide. This was few days ago and I was trying to digest how to explain the difference. To me. By switching from the 140 to the 130 tails. It felt like going from the 1180 HA to the 880 in terms of agility and playfulness. Can't wait to get more time in the surf with this combo.
Look at Kai's board in his new video. Looks like the tail of that board is wider. Almost Omen Flux ish shape. Board appears to be slightly wider. Cool. Fits those waves well.
I would look into Dr Stuart McGill and his book Back Mechanic. He is world class and no nonsense and does not beleive in surgery. Also one of his client Brian Carroll and his book Gift of Injury. He was a world class powerlifter that followed Dr Mcgill's methods and came back to lift more. I had ruptured L5 S1. Took years to recover fully. But I have been following the things I learned in Back Mechanic to barely have any issues. For the cost of those 2 books, it would be worth your time before committing to anything else.