RE: Yet another question about a board
Unfortunately, you will loose some early planing as well as stability with the narrower (and narrower tail especially) Carve or Futura in the
122 -133 liter size range.
Since you are a lightweight @ 66 Kg (145.5 lbs.) you can get the same sort of performancfe from the 122 liter that other heavier sailors get with the 133.
Compared to your 80 cm wide (52.7 cm 1 foot off) Go 139, the Carve/Futura 122 liter is going to be around 68.5 cm wide with a 43.8 cm 1 foot off measurement.
This narrower width is going to take away some early planing performance in 8-12 knots.
But it may add a knot or 2 on the high end of the wind range for the board.
What size sails are you currently using on your GO 139?
The current Carve 122 seems to handle an 8.0- 8.5 m2 sails pretty well, but 6.5- 7.5 m2 is really the sweet spot, so you will need rigs in the full range from 6.5 -8.0 m2 to get the most performance potential out of the board.
You are lightweight and fit, so you should make the transition pretty easily, and then be on your way to even smaller hi-performance boards.
Hope this helps,