RE: looking for advice buying a new board
I think it depends on if you want a really wide range board (the GO 139 which is really not just a beginner board as someone has suggested) or if you want something a bit more "turny" with a more limited range.
The GO 139 will handle larger (and smaller) sails a bit better than the Carve 133.
Once you get used to the slightly wider (80 cm) Go 139, you will be able to get planing somewhat earlier (same sail size) than you can on the 71.5 cm wide Carve 133.
If you learn a bit from the formula racers (who sail really wide 100 cm wide boards in pretty outrageous conditions...like 25 knots with a 9.0 m2 + rig) you can get quite a bit of high wind performance from the GO 139.
It's just a matter of tuning for the conditions (up to a point of course) to keep the little GO "on the water".
In conditions that suit the high end range of the GO 139. you are going to begin to experience some of the same "too much wind for the range of the board" issues with the Carve 133 unless you are one very heavy sailor.
If you want the largest range, and then a smaller board to cover the 20 knots+ plus range, the GO 139 would be a good place to start your quiver.
Anyone who feels the newer GO boards are only for beginners probably hasn't sailed one fully powered up in 15-22 knots of wind on a 6.5=-7.5 m2 rig.
If you have really big chop and very rough conditions, then the Carve makes a bit more sense.
Hope this helps,