Filipe it all depends on every case. In mine, I'm 87Kgs today (whatever the scale says) and got myself a 5'6". Used to ride 30lts boards I was a little apprehensive about going down in volume, but the shape of the board is so unique that it allows to paddle surprisingly well despite this fact. The wider nose and overall rail line, mixed with the volume distribution allows fo the board to float really well.
If you want to play safe the 5'8" will do the job.Remember this board excel on better waves. But the board floats me plenty even on a 6/4suit with all the trimmings
I'm 88kg and 5'11" and my 5'6" Vanguard goes great for me. It doesn't paddle into grovel as well as high volume fish designs but its not designed for small and weak waves, its ideally a replacement for your daily driver in good waves.
It paddles in a lot better than a typical high performance shortboard at the same volume due to the different physics of the shape moving through the water.