Hi Leroy82 ,
I am 1m89 and +/-110kg and I have a custom Hipster Twin 9'10 x 33' and 170 litres.
www.seabreeze.com.au/forums/Stand-Up-Paddle/Review/French-Smik-Hipster-Twin-CustomBefore this board my smallest board was a 10'5 x 32'3/4 and 190 liters with a longboard shape.
I didn't want to go on the 9'3 because I wanted to ensure very good stability and comfort to be able to stay in the water for a very long time (2h30/3h) without getting too tired.
And really I'm super happy with this custom, as I wrote in my post the adaptation only took me a few minutes.
Given the shape of your Jackrabbit, its width (31') and its volume (159litres) I think you have 2 options, either the 8'10 x 32' and 145 liters or the 9'3 x 33' and 153 litres.
Now to see how you feel on your ECS, if you're good on it and it seems "comfortable" to you, I think you should listen to Scotty and go on an 8'10, if you're on the edge of stability and you're looking for a little more comfort leaves on the 9'3.
But really you can trust Scotty with your eyes closed, he knows his boards and his shapes better than anyone, you really won't be disappointed!!!