I think the amount of rocker in your board has more impact than your weight etc.
On my Mutant i can use the 20mX2 under 10 knots (jumping, upwind). on my littleTT with much more rocker, I need another 4 knots and even then I feel like I am slogging. It's a different riding style.
With a flat rocker board you get power from speed, with a bendy TT you are using the board to slow you down when super lit.
For example if the wind was steady 16 knots - I could go the 14m X2 and Mutant, or the 20mX2 and tiny TT. I would probab ly be powered sim ilarly on bothg - but with more bar pressure and less speed on the 20m.
The Advantage of the 20m and TT in this wind is big, floaty transitions and pop whenever you want it. The disadvantage is that you get tired pretty quickly as it takes more work.