I probably went a little overboard, but I am using 3/16 7x19 galvanized wire rope. The stainless was too much for me.
The 7x7 you reference will be a bit stiffer than the 7x19. I also would not recommend the coated, I have read problems with coated cable slipping at your wire rope clips.
I will use two wire rope clips at each end with a thimble. At the anchored end I will have a 3/8 turnbuckle with 3/8 quick links. I bought 36" auger anchors for carport tie downs for my anchor.
The top it will be connected by a 3/8 quick link.
My mega tree is 20ft but it gets windy here. I was going to have 3 guy wires, but couldn't find a good attachment for a 3 guy wire system, so I went with 4.