The Shroom is a big board for each size.
I am 72, 106 kg and I also have an 8'3.
I borrowed an 8'7 for a season and found it too big.
The 8'7 surfed ok and was super stable, so if stability is your goal, then maybe the 8'7
But the 8'3 will surf more in line with what this is designed for.
Here's a vid of my 8'3, showing detailed first paddle, for a good look at stability and first surfs.
Short Shroom look (one wave from above, but a decent look at how flowing it surfs
I also have the 9'2 Skate. I use it more than the Shroom, because it fits more conditions.
If surfing waves over 4'' on the Shroom, I need to scrub speed off, to throw a hard turn, because of the wide tail.
The Skate turns different from most boards. It is best when "banging" it back and forth... much like kick turns on a skateboard on a flat parking lot.
Video showing Skating an average day.
The 9'2 Skate and 8'3 Shroom are the correct sizes for me.
The Skate will paddle much better
The Shroom will snap tighter arcs
Both good, so depends on your goals