This is a common question for newbies interested in "stability".
I would like to share a quick test that you may want to try. I use this test to decide what skiboards to let new riders try out in our growing collection. It has no scientific basis and may sound strange, but it seems to provide some guidance for a good match.
In a safe area in your home, where you can hang onto something, and without any gear on, stand on one foot and balance yourself. Then close both your eyes, let go of your support, and see if you can stay balanced on one foot. If you can stay balanced on one foot with your eyes closed, then you would be fine on a shorter board (for your height and weight). But if you find it difficult to hold your balance with your eyes closed select a longer board which will provide more front to back stability.
As Valmorel has stated:
"Skiboards cant tell how tall you are, only your weight huh? Well, literally true, but pragmatically false. All skis/skiboards flow down the hill in a series of micro stops and accellerations as they run over the uneven terrain. The body feels this as a constant feeling of 'lean back/lean forward' to maintain balance. The longer the board, the smoother they ride, and the taller the rider, the greater the induced leverage from rider height. This induced leverage gives the quads a real work out, so, in general, tall riders will get less tired on longer smoother riding boards.
I notice a series of marked steps up in this effect as I go from 99 to 110 to 120 etc."